T h e I n s t i t u t i o n o f P r o d u c t i o n E n g i n e e r s J o u r n a l

V O L . 3 8 N O . 1 0 O C T O B E R , 1 9 5 9

THE ECONOMICS OF

TRANSFER PRESSING

by LOUIS SCHULER

Managing Director,

L. Schuler A.G., Goeppingen

A Paper presented

to the Midlands Region

of The Institution of

Production Engineers,

IOth December, 1958.

THE manufacture of sheet metal components bychipless forming is normally carried out by means

of a series of successive operations, which generallyinclude blanking, drawing, bending,^mbossing, andso forth. The number of operations used for themanufacture of a given component basically dependsupon the raw material employed and the shape ofthe component itself. In many cases, normalising hasto be employed between operations so that workhardening and brittleness of the material isneutralised.

Production of a component on individual machinesmeans that this component has to be fed by handto each machine. In order to avoid this manualfeeding, machines which execute a series of opera-tions (the component being automatically conveyedfrom one tool to the next) were developed manyyears ago.

Fig. 1 shows the evolution of transfer presses fromearliest days to the latest fully-automatic press withvery high production capabilities. Even today, thereare many varying opinions concerning the efficiencyof transfer presses. Whilst the transfer press waspreviously considered as a machine suitable only formass production, this conception has now beenmodified considerably. Transfer presses can today,in many cases, be efficiently employed for the pro-duction of medium-sized batches. This is the resultof purposeful development toward high output, rapidtool changing and safety in operation.

535

Fig. 1. The evolution of the transfer press. ,

(Left) 1957.

536

Particularly from the point of view of production,other factors play an important role. The majorconsiderations here are saving of floor space as com-pared with single press lines, and the eliminationof operations such as inter-stage normalising, picklingand spinning, etc. The rapid and efficient materialthroughput in a given production cycle, raw materialto the finished product, and the complete avoidanceof damage to components during production, arealso points well worth bearing in mind.

In order to assess whether a component can bemore efficiently manufactured in a transfer press ascompared with single presses, many basic considera-tions have to be taken into account; the number ofoperations, total number of components required,and rate of production, are obviously of majorimportance. The number of operations depends onthe particular form of a component, the material ofwhich the component is to be made, and the dimen-sional limits and required surface finish. When acomponent is of complex design, and the rawmaterial of which it is to be made is difficult topress-work, then the number of operations necessaryfor the production of this component obviouslyincreases. In addition, factors such as small dimen-sional limits or the requirement of high surface finishcan also necessitate an increase in the number ofoperations.

For instance, because of the narrow dimensionallimits and the required high quality of surface finish

on a relatively simple component, two external aswell as two internal shaving operations had to beincorporated, in addition to the more normal opera-tions. This resulted in more economical productionof this component on a transfer press, as comparedwith individual presses. The upper component shownin Fig. 2 was difficult to manufacture because of therequired close tolerances, whilst the lower portionof the same illustration shows the stages of a com-ponent in which both form and the tolerancesrequired presented special difficulties. The componentpossessed tolerances of the order of .001 in. Blankswere cut by twin-row stagger stamping, and thematerial saving thereby was approximately 7%.

With drawn components, the wall thickness reduc-tion at the punch draw radius often necessitatesconsiderable extra working; particularly so when acertain standard of surface finish is to be reached.Sometimes grinding, polishing or other non-pressoperations cannot be avoided, but much morefavourable conditions can be achieved when theindividual operations can be carried out withoutsevere changes of form from operation to operation.The necessity for additional work in connectionwith surface finishing can often be obviated bycarrying out the production of a component in morestages than those which would usually be acceptedas conventional deep drawing practice. The produc-tion engineer would be more ready to accept moreoperations when use could be made of a transfer

Fig. 2. Operation sequence.

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60 000

i 1 1 1 1 1 1 1 1 1 ! nIn on* pass from coil stock to finished Housing made to tolerances of.002"(0,05 mm)

32 40 hours

Working- hours

F.g. 3. Output on transfer press compared with single presses.

press which offers the facilities of one or moreadditional operations without the penalty of lowerproduction or more individual presses, and theseadditional operations will be particularly welcome toavoid annealing and bonderising operations. In thisconnection, it may be useful to mention that by theuse of additional operations it is sometimes possibleto employ a material with inferior drawing quality.

I would now like to consider in some detail thecalculation of the efficiency of producing a housingon a transfer press. These calculations, for the sakeof clarity, have been considerably simplified. Accounthas been taken of tool costs and operating costs only,without insisting on the vital basic assumption ofequal output. As Fig. 3 shows, the production ofthis component on single presses is about half theoutput of a transfer press, and it must therefore beemphasised that the transfer press is only partiallyloaded. This, of course, tends to show the transferJMTSS to be less efficient than is actually the case underpractical conditions. In addition to this, otheradvantages in favour of the transfer press, such asspace saving, reduction of normalising operations orsurface finishing operations, as well as the rapidmaterial flow and considerably lower scrap percentage,and elimination of intermediate storage, are notnhown in this consideration, and the transfer press is

thus further handicapped as compared with single-operation presses.

The manufacture of the housing shown is earnedout on single presses as well as on transfer presseswith 11 stations.

The costs of the calculation of efficiency in Fig. 4are taken as the hourly rate of pay of a skilled metalworker. By adopting this standard for unit cost, theresultant figures are independent of the currencies

used in various countries. Apart from the smallrelative differences from country to country in rela-tion to standards of living, the ratio between variouscosts can therefore be established.

If a batch size of 10,000 components is taken, thatis, if tool changes are executed after each run of10,000 components, then the operating costs, perbatch, are 719 units in the case of single operationpresses. These operating costs are built up from thecost of actual forming or shaping the component in11 presses, the cost of setting time for the tools, andthe cost of transport between successive machines.

In the case of a transfer press, however, theoperating costs are merely made up of the cost offorming or shaping the component, and the cost ofactually setting the tools in the press; the comparativefigure is only 253 units. Thus in spite of thisrelatively adverse comparison, reasons for which have

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been outlined earlier, operating costs of the transfeipress lie considerably below the cost of using singlepresses. On the other hand, tool costs themselves inthe case of this set of tools for transfer presses are7,300 units, as compared with 5,700 units for toolcosts if a similar set of tools is to be used in singlepresses. Generally speaking, the tool costs for transferpress tools are approximately one-quarter higher thanthe cost of a comparable set of tools for singleoperation presses.

Fig. 4 shows the increase of manufacturing costs,made up of tool costs and operating costs, on in-creasing the number of components required. The fulllines are for batch sizes of 10,000 components. Fromthe diagram it is seen that manufacturing costs onthe transfer press, upwards of a quantity of 34,000components, are less than the costs of manufacturingcomponents on single presses. If a batch of 10,000is therefore set up more than three times, the transferpress manufactures these components at a lower cost.

The actual quantity of components, above whichthe transfer press becomes more efficient than singlepresses, can therefore be evaluated from the equationgiven in the lower right-hand corner of Fig. 4. Toobtain this number of components, multiply thebatch size by a factor which is obtained from thedifference between tool costs and the difference ofincrease in operating costs.

In actual practice, the transfer press becomesefficient at a considerably lower total number ofcomponents than is indicated from this equation, asthe transfer press inherently possesses a higher outputwhen compared with single presses, in addition to a

number of advantages which have previously beenindicated. If, for instance, the component shown inFig. 4 were to be manufactured on single presses at arate of ouput comparable with that of the transferpress, say, 1,000 components per hour, then it wouldbe necessary either to boost and partially automatethe single line presses, or to duplicate the whole lineof single presses.

With a duplicate line of presses, the tool coststhemselves would be doubled, as would the operatingcosts. It is therefore clear that the transfer presswould in any event produce the components moreeconomically. When a line of single presses is auto-mated, insofar as this is possible to obtain a form ofsemi-automatic flow through the press line, theactual costs of forming or shaping the component arelowered, but in any event it is not possible to reachthe same low level of these costs as is obtained on atransfer press. On the other hand, both the toolsetting times, together with tools and auxiliary equip-ment costs, will be greater than similar costs on atransfer press.

It is often stated that the transfer press requiresextended tool-setting times. In practice, however, ithas been shown repeatedly that the setting time fortools in a line of single presses is considerably higherthan the time required to set tools in a transfer press.In practice, it is also found that the cost of tool-settingin single presses is higher than tool-setting costs in atransfer press when a similar component is beingconsidered in both cases. This in fact is indicatedbv the previous example. It is therefore clear thatefficient production can be achieved even if the total

Number of components

Output per hour

Manufacturing costs per hour and machine

Setting time for 11 operations

Transport for 10000 components

Tool costs

Operating costs for batch of 10 000 components.

Manufacturing costs 15 « 4 «11 •

Setting time

Transport

Single Presses

660 components

4 units

48 "

11

5700 "

660 units

. 4 8

11 •

Transfer Press160 tons

1000

23

23

-

7300

10*0- 230

23

__

isT

Calculation of number of components

with same costs of production.

difference of tool costs

difference of operating costsbatch size - number of components

7300-5700 . 1OOoo - 3 * 0 0 0 components719- 253

All costs ore given as a multiple of the hourly rote of pay for a skilled Metal Worker (-units)

Fig. 4. Production costs of housings.

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requirements of components is made in small batchsizes, the tools for which are set up in the transferpress at intervals.

This point is worth bearing in mind, as it isgenerally not expedient to manufacture given items inlarge batch quantities because this may necessitatecarrying unnecessarily large stocks of components,representing idle capital. Such storing of finishedcomponents would, of course, have a detrimentaleffect on the overall price of the manufacturedarticle. In addition to this, in many cases it is ofadvantage that components should be manufacturedin small batch quantities so that flexibility con-cerning product changes is retained, without thepossibility of having to scrap large stocks of com-ponents which may become obsolete.

I am convinced that there are few productionengineers amongst us who have not at some time intheir career torn their trouser-legs on the sharpedges of tea-chests. Apart from tea-chests, there aremany more modern methods of storing componentsbetween successive stages of manufacture on a singleline of individual presses. On a transfer press,however, this inter-stage storage and its associatedevils, completely disappears; the material flowthrough the production of a given component is

Fig. 5. Forces and bending moments acting during loadconditions with a given component.

almost wholly rationalised in this respect, and thecost of storing inter-stage components completelyeliminated.

Even with large transfer presses producing atrelatively low speeds, the time required for the pro-duction of one component is less than one minute.This applies even when transfer presses have as manyas 14 stations. The output of a transfer press is equalto the number of strokes per minute, and at eachstroke of the press one finished component is manu-factured.

elimination of age-hardeningThis rapid flow of work through a production cycle

is particularly useful when material which tends toage-harden is being used. Because of this rapidsuccession of operation, age-hardening is eliminated.Chiefly for this reason, normalising betweenoperations becomes unnecessary. An additionaladvantage of this rapid flow of material in a transferpress, is in relation to aluminium alloys. Thesematerials can generally be normalised just beforecommencing production, so that the necessaryforming or shaping can take place within the transferpress. Age-hardening then sets in only after the com-ponent has been completed, and the hardness of thealuminium alloy which may be necessary for aparticular component can then be reached duringstorage after manufacture.

From the overall economic point of view, it isworth bearing in mind that faulty material suppliescan very rapidly be detected in transfer presses. Ifthe quality of the sheet is not up to specification,this may not be noticed until the last operation of aseries of individual press operations. By this timeconsiderable quantities of components may alreadyhave been produced on earlier operations in the singlepresses, which may have to be rectified or normalisedbefore these components can be used. This will, ofcourse, create additional unexpected costs.

Risks of this kind are completely eliminated in thetransfer press because of the rapid material flow fromstation to station. The first few finished componentswill clearly indicate material faults.

It is frequently noted that when components aremanufactured on transfer presses, as opposed toindividual presses, normalising operations areeliminated. The chief reason for this is the lack oftime for age-hardening during the work cycle.A contributory factor towards the eliminationof normalising is that more press operationscan be incorporated in the transfer press. Whenusing individual presses, operating costs rise appreci-ably with increased numbers of operations, as notonly the fixed charges, such as machine costs and toolcosts, increase, but also the actual operating costs.In fact, this increase is proportional to the numberof components produced and obviously considerablyaffects the part cost.

With transfer presses, however, the only increasein cost is in fixed costs, particularly when one candisregard the very small additional charge arisingfrom setting extra tools in the transfer press. These

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costs hardly affect the part cost even with average-sized batches; but, on the other hand, the savings incosts by eliminating special normalising or heattreating and pickling operations are quite consider-able. A further advantage is that when it is necessaryfor a material to be bonderised, this layer of phos-phates will be retained on the component untilcompletion and will not be destroyed during the heattreatment or normalising.

Another considerable advantage of transfer pressesas compared with single presses is low floor spacerequirements. A medium-sized transfer press, togetherwith its auxiliary equipment such as decoilers andlevelling units, requires a floor area of approximately200 sq. ft.

To produce the same component in single presses,nine individual presses would be required to give asimilar number of operations. Moreover, in order to'match the output of the transfer press of approxi-mately 900 components per hour, two lines ofindividual presses would be required. The floor areafor these two lines would be of the order of 1,100sq. ft. An additional factor in this connection is thatmanufacture of components on single presses, inspite of guards and other safety devices, can lead tomore accidents, which are virtually eliminated in afully-automatic transfer press.

influence of designIn the considerations so far mentioned concerning

the economics of transfer presses, technical pointshave not been dealt with. The mechanical design oftransfer presses and associated sets of tools offer quiteconsiderable advantages for the economic use ofthese machines. Therefore, I would like to discusssome of the basic factors influencing the design oftransfer presses.

The drive of the transfer press is accommodatedin the headpiece; the motor, through an infinitelyvariable gearbox, drives the flywheel. The flywheelitself is mounted on a lay-shaft and, by means of arapid acting clutch and brake, can be connectedor disconnected from this lay-shaft. The actuationof the clutch and brake unit is such as to permitvirtually instant stopping of the ram in any positionof the stroke. The lay-shaft then drives both pairsof reduction gear wheels (Fig. 5) which in turn driveboth eccentrics and Pitmans, which in turn actuatethe ram. This general arrangement of the driveresults in a short path of flow of forces and ensuresa strong drive connection. Even with greatlyasymmetrical loading, differential torsion at theeccentric drives does not arise. Both twin gear wheeleccentric drives are directly above the uprights ofthe press, and are mounted between the anchorcolumns inside the uprights. From this arrangementaccrue two vital advantageous design factors : firstly,there are no bending moments in the crown of thepress ; and, secondly, the anchor columns them-selves are always loaded in pure tension.

The illustration shows the individual loads at eachtool station for a particular set of tools, and also theresulting bending moments from this load condition.

The bending moments which arise are relativelysmall, even though the load diagram is compara-tively awkward. Deflection which arises due tobending moments is therefore also small. Theblanking station is incorporated inside the left-handupright, directly below the point at which the lowerend of the left-hand Pitman acts in the ram. Thisarrangement ensures that the blanking tool stationis not affected by bending moments. The deflectionat the blanking station is so small that the life of thecutting tools is at a maximum.

Within the right-hand upright a special em-bossing station is incorporated. When this positionis loaded with a maximum pressure, the resultingdeflection is negligibly small, whilst bendingmoments due to this load do not arise at all. Thisarrangement permits the use of the earliertool stations in the transfer press for planishingoperations. In addition to this it must bementioned that the loads arising, not only in theblanking station but also in this embossing station,do not influence the loads occurring in the inter-mediate tool stations.

The illustration also shows that the ram is guidedfour times at each side, resulting in a total of eightlong guides. Extremely precise adjustment of theseguides is effected by means of wedges which ensureexact guiding of the ram, even with severely asym-metrical loading.

Transfer presses can be fed automatically withcoil, with strips, and also with pre-cut blanks. Fig. 6shows various types of feeding equipment fortransfer presses. The top illustration is of a de-coiling unit. The stock then passes through alevelling unit and is fed forward to the press. Betweenthe leveller and the press a short loop is normallyarranged, the depth of which is maintained constantwithin certain limits by means of a mechanicalfeeler arm. The decoiler itself is so arranged thatwhilst the material is being drawn from a coil onone side of the head of the decoiler, the second headis ready for loading with a new coil. The bottomleft-hand illustration is of a strip feed mechanismsuitable for strip lengths of up to 142 in. Thismechanism feeds strip after strip to the press with-out the necessity for an idle stroke of the ram ofthe press between successive strips.

The right-hand bottom illustration is of a singleblank feed unit, which feeds from the stack of pre-cut blanks to an extension of the gripper railsfeeding the tool stations in the press. Of the threeblank stack positions on the dial feed plate, two arenormally kept full whilst the third is being refilled.As soon as a stack is empty, the dial feed plate isrotated through a third of a revolution to bringthe next stack into line with the pick-up head. Bothstrips and blanks are always automatically checkedwithin the press to ensure that only one sheet thick-ness is being fed. Special arrangements for fully-automatic magazine feeds for the feeding of pre-blanked and drawn components, or partially bentcomponents, have also been designed. This type offeed sometimes finds a special application when the

541

fe. JMa»fci**- h

%' sfcer-jr i f •

Fig. 6. On the left is shown a decoiling unit, and below

a single blank feed unit, as described on page 541.

(Above) A strip feed mechanism for strip

lengths of up to 142 in.

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parts to be fed may be manufactured from the wastesheet resulting from another operation.

Coil stock and strip material is fed to the blankingstation by means of a double-sided precision roll feed,in front of the infeed rollers of which cleaning andpre-lubricating equipment is fitted. Single-row, ormulti-row, stagger blanking can be carried out.Should stagger blanking be required, then theblanking station is arranged outside the main left-hand upright of the press.

Fig. / shows a typical stagger stamping mechanismwhich, by cam actuation, reciprocates the blankingtool on its slipper at right-angles to the direction ofthe stock feed. The mechanism positively locates theblanking tool in each of the idle motion cam positions,and hence precise blanking positions are achieved.Reciprocating weights and therefore inertia loads onthis type of mechanism are maintained as low aspossible. Resetting for a different pitch of cross-feed iseffected rapidly and easi y by means of spindles.

The second pair of rollers of the roll feed is locatedbehind the blanking tool for the outfeed motion ofthe shred towards the scrap cutter. The scrap cutteritself is adjustable along the line of stock feed so thatthe scrap can be cut at its weakest section.

Feeding of the component from tool station to toolstation within the transfer press is effected by meansof grippers. It is vital that the motion of the grippersnot on>y ensures positive feeding of the componentsfrom one tool station to the next, but also that at the

start and finish of this motion the actual speed of thegrippers must be zero; otherwise the danger wouldexist that when the grippers open, the componentitself would still possess some momentum which wouldtend to dislodge the component from its correctposition on the top surface of the bottom tools.

Fig. 8 shows the drive for transverse motion of thegripper rails. One complete revolution of the eccen-trics for the ram motion corresponds to one cycle ofthe chain. The s iders attached to the chain movethe transverse slotted link up and down, and this linkin turn actuates the left and right-hand rods. Atthe lower end of these rods the racks move thepinions, which in turn give an oscillating 180° backand forth motion to crank levers from one deadcentre position to the other. These levers, through aconnecting rod, move the gripper rails in the trans-verse direction. The combination of slider, rack andcrank mechanisms ensures positive and shock-freefeeding of the components, because not only the rackand pinion motion, but also the crank and con-rodmotion, start and end each cycle with zero velocity.

The combination of these motions results in par-ticularly gentle acceleration and retardation of thegripper rail motion. Closing and opening of thegrippers is effected by means of a cam attached tothe ram. Both gripper closing and transverse grippermotions are safeguarded against overloading. Thisoverload safety device is electrically controlled so thatif an obstruction should occur to the gripper railmotion, the press is immediately stopped, before anyfurther damage could result in a different position.Apart from these safety devices, the correctpositioning of the components at each tool station ischecked electrically. Feeler fingers immediatelyindicate mislocation of a component in any given tool

Fig. 7. Equipment for stagger blanking.

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Fig. 8. Drive for transverse motion of gripperrails.

station, and the ram motion is again stopped instan-taneously. By these means faults, such as failure ofejection of a component from any top tool, areimmediately detected, and the damage which afurther stroke of the ram could cause is completelyobviated. In order to enable the ram motion to bestopped in any position, a rapid acting friction discclutch and brake is used. The actuation of the brakeand clutch is electro-pneumatic.

This high speed clutch and brake unit ensuresimmediate stopping of the ram without the damagingeffects which may take place if the ram were to runon any distance after declutching and applying thebrake. This is of particular advantage when a jamoccurs, or when one of the uprights is overloaded.Incidentally, an overload above a pre-set maximumload in any upright brings into immediate operationanother safety device which stops the ram.

Similarly, further safety devices stop the press if theelectrical supply fails, if the air line pressure dropsbelow a permissible minimum, or if the oil pressure inthe automatic oil feed lines fal's below a certainvalue.

Whenever a fault occurs or an overload takes place,this fault is immediately indicated either by awarning lamp or by the position of the pointer of theoverload device.

From the foregoing description it may appear thatthe press is all too liable to light up like a Christmastree and be in a permanently stopped position. Inpractice, however, the chief object still remains, thatis, to have the transfer press running continuouslyand also to be able to stop it very quickly inemergency.

The rapid acting clutch and brake unit is foundvery useful when tool setting, because the ram can bepositioned very accurately. Rapid tool changing is ofgreat importance, particularly so with small batch

sizes. Depending on the total weight of a set of tools,either one combined bolster plate or two are used tomount the bottom tools, so that individual tools neednot be removed or set singly. Fig. 9 shows this formof tool set.

When dismantling a set of tools from the press, thetop tools are first lowered on to the bottom tools,then the top tools and bottom tools fixed to theirbolster plates are removed together from the press.This operation is generally effected by the use offork lift trucks.

When inserting a set of tools into the transfer press,again a fork lift truck will lower the bo.ster plate onto the press table, and the bolster plates are thenmoved into position against positive keys or stopsfixed to the bed of the press. Height setting data fortop tool height position is normally maintained on adata sheet. The normal procedure is as follows:

Individual positive ejectors in the ram are dis-engaged. The ram is moved into the top dead centreposition. The tools are then inserted into the press.Then individual top tool holder heights are adjustedeither by means of a ratchet lever, or by means of anelectrically-driven rapid setting attachment. Heightsettings are checked on scale readings on the indi-vidual top tool holders; these scale readings onceestablished are obtained from the data sheet. Thenthe ram is lowered to a point where the top toolstalks reach into the tool holder holes. Top tools arethen clamped up in the conventional manner. Thenthe necessary air pressure for each individual pneu-matic cushion in the bed has to be set. This iseffected by means of the handwheels, seen in thelower part of the illustration, and the mano-meters which indicate the pressures. Again fromprevious experience, individual stage air pressures forthe cushions are taken from the data sheet.

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After this, the positive ejectors are set, again tosca.es and previously established values. When thiswork has been completed the pair of grdpper rails,complete with grippers and safety feeler ringers, arefitted over the bottom tools and into the gripper raildrive mechanism. After this, the separate blankingtool is mounted between the left-hand uprights, theposition of the scrap cutter is reset, and the stock forthe production of the component is fed into the rollfeed.

The first cycle of the press can then take place, andnecessary minor corrections may be carried out totop tool height settings or ejector settings.

The efficiency of a transfer press can often beconsiderably increased by designing the components,or laying out the stages in the transfer press, topermit standardisation of components. By these meanssome of the operations in a transfer press can be usedfor different components. All the necessary toolsshould be mounted on a combined bolster plate,although only a portion of them are used for theproduction of any given component. This wouldresult in very low tool changing times.

In some instances it is possible to maintain thesame external form for two different components,particulany so in cases where different hole piercingis necessary. In such cases tool changing is completelyeliminated, and all that is necessary is to lift one ormore piercing top tools out of engagement, so thatthose particular tools do not perform any work on thecomponent. The operations on the part will then becarried out, and the unnecessary tools will merelybe by-passed. In cases where lifting the top tool isinsufficient, it is of course possible to remove only thetop tool from the press. In such cases changing thepress from the production of one part to the other iseffected within minutes. This example demonstratesthe effectiveness of standardised product designwithin an organisation.

Fig. 9. Tool setting.

Even the best transfer press cannot functionrationally if, due to inexperience, mistakes have beenmade in tool design. Transfer press tools are designedwith different basic assumptions as compared withconventional press tools. It is vital to eliminate fromthe very beginning operations which are of a riskynature. Individual tools (as previously indicated)should be kept as simple as possible, so that the com-ponents will not lead to frequent jams in one tool.It is important that successive stages are so arrangedthat effective and positive working of each individualtool is achieved, and also that at no single point is themetal which is being worked so highly stressed as toreduce the life of the tool. Similarly this will obviatefrequent stopping of the press because of localisedrepeated trouble. For instance, at a cutting stationthe remaining metal thickness in the componentshould be sufficiently strong to ensure that tearing ofthe material does not take place. In order to avoidthis, it is better to carry out a given amount of cutting"in two successive stages, than to do all the cuttingwork in one tool and thereby risk fractures in thecomponent. Also, heavily loaded tool stations shouldbe so arranged as to be positioned near the uprights,rather than at the centre of the press. Such opera-tions, for instance embossing, should wheneverpossible be carried out in a special embossing stationtowards the end of the total number of operations ona component.

During the design of transfer press tools, particularattention should be paid to the fact that these toolsare intended for mass production. The very design

545

of each tool, and the selection of tool steels for itemsin tools which slide against each other, has to becarefully considered. The build-up of a tool shouldbe such that certain steels which may be subject towear can be readily interchanged without having toremove from the press either the top tool or thebottom too . Methods of removal of scrap areparticularly worthy of detailed attention. Scrap, suchas piercing slugs or trimmed shreds, should be re-moved positively. When scrap chutes have to beincorporated in the tools, the scrap should beremoved by means of positively acting levers or com-pressed air.

Springs for the actuation of positive motions ofparts of tooling are best avoided. All such motionsinside the tools, as for instance ejection motions orslider side-piercing motions, should, wheneverpossible, be effected by means of cranked cams withpositive return motion. Incidentally, it is vital thatthe fixing of cranked cams should permit a shearing-off of the cams if a fault develops an overload, sothat the cam is broken off before doing considerabledamage to the tool.

All drawing tools must be fitted with provisionfor the supply of coolants or lubricating fluids. Suchconnections are fitted by means of pipes to drilledducts inside the top tool. Transfer presses areequipped with a return flow system for these fluids,the flow being achieved by means of an independentlydriven pump, collector troughs, filters and sieves.

In conclusion, I would like to give some indication,by means of two illustrations, of some of the manyand varied shapes of components which can be manu-factured on transfer presses. Fig. 10 shows various

operation sequences of circular and irregular com*ponents on transfer presses, and demonstrates thatconsiderable form changes are possible without inter-mediate normalising. Fig. 11 shows further transferpress parts.

I have attempted to give you some small indicationof the various factors which have to be consideredwhen evaluating the economics of whether a givenpart is to be manufactured on a transfer press, oron individual presses. When the components to bemanufactured are of such a design as to lend them-selves to manufacture by individual successive pressoperations, then it has been seen that the transferpress can be used efficiently, even if only tool costsand production costs are considered.

The economics of a transfer press become evenmore advantageous when other factors concerningthe efficiency of the machine are drawn into con-sideration, such as greater output, lower scrappercentage, elimination of normalising and pickling,saving in floor area, faster material throughput,elimination of intermediate storage, reduced quantityof finished components in store, safe operation andaccident prevention, and other similar factors.

With these acknowledged facts in mind, oneindustrial concern concentrated the whole of itsproduction on transfer presses more than 20 yearsago. This factory possessed 96 transfer presses whichenabled even small batch sizes to be manufacturedwith considerable economy. This fact will illustratebetter than words that the manufacture of com-ponents on transfer presses has proved itself, and thatthe efficient use of transfer presses could be employedfar more widely than is usually expected.

Fig. 10. Operation sequences in production on transfer presses.

546

Fig. 11. Operation sequences in production on transfer presses.

The author of this Paper was educated at the University ofFrankfurt, the Sorbonne and I'Ecole pour Arts et Metiers inParis, and the University of London.

After obtaining workshop experience at J. M. Voith,Heidenheim, and United Shoe Machinery, Frankfurt, Herr Schulerstudied press and tool construction at the Citroen Works inParis, and electrical engineering at Alsthom, Clichy. Furtherworkshop training was obtained at various factories in England,and he subsequently worked at the Intertobis, Amsterdam. Hewas later invited to join Film Sonores Tobis in Paris as BusinessManager.

In 1934, Herr Schuler took up his present appointment asManaging Director of L. Schuler, A.G., Goeppingen, the firmfounded by his great-grandfather, and which pioneered thebuilding of power presses.

He has travelled widely in Europe and overseas, is a Memberof the Italian Chamber of Commerce for Germany, and of theAdvisory Council of the Bad-Wuertt section of the Rhein-MainBank.

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