ScienceDirect. Direct Drive of 25 MN Mechanical Forging Press

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1 Available olie at ScieceDirect Procedia Egieerig (25 ) th DAAA Iteratioal Symposium o Itelliget aufacturig ad Automatio, DAAA 24 Direct Drive of 25 N echaical Forgig Press Ja Hlaváč, ila Čechura* Uiversity of West Bohemia, Uiverzití 8, 36 4 Plzeň, Czech Republic Abstract I the brach of forgig presses there are ew oes with direct drive. Our aim was to fid out its possibility ad to validate its properties ad fuctioality. echaical forgig sigle poit press with a omial force of 25 N is selected for the example of direct-drive this is a more powerful tha was ever produced. The proposed direct drive is solved by pair of torque motors. These are coected with eccetric shaft via a gear drive, because of eed to reduce speed. The paper gives the egieerig process, icludig determiatio of the time of the stroke. We tried to discus a questios about efficiecy i this paper. 25 The Authors. Published by Elsevier by Elsevier Ltd. This Ltd. is a ope access article uder the CC BY-NC-ND licese Peer-review ( uder resposibility of DAAA Iteratioal Viea. Peer-review uder resposibility of DAAA Iteratioal Viea Keywords: formig machie; direct drive; forgig; torque motor. Itroductio [], [2] The issue of direct drive of formig machie is i focus i the Cetre of research i the machie desig (CVTS) at the Faculty of echaical Egieerig Uiversity of West Bohemia i Pilse for a log time. The large-scale deploymet i the crak presses desig this drive collide with poor performace ad high cost of special torque motors ad especially with the iability to quickly ad adequately capacitive accumulatio of electricity. Time progressed ad the deploymet of direct drive has become more available, although there still remais a questio about its beefits. A example of direct drive forgig press might be Schuler GROUP press PK SDT 6 [2], which is i operatio i forge ŠKODA AUTO. Amog the suggested advatages of direct drive belogs shorteig of uproductive time, * Correspodig author. Tel.: ; fax: address: jhlavac@rti.zcu.cz The Authors. Published by Elsevier Ltd. This is a ope access article uder the CC BY-NC-ND licese ( Peer-review uder resposibility of DAAA Iteratioal Viea doi:.6/j.proeg

2 Ja Hlaváč ad ila Čechura / Procedia Egieerig (25 ) which is positively reflected i the productivity of the press (the umber of strokes per miute). Aother of the perceived advatages that coected with direct drive i geeral, is a reductio of eergy cosumptio by removig compoets such as clutches, brakes, belt drive, etc. Forgig press Schuler PK SDT 6 is a proof that techical solutios exist. Therefore we decided to project direct drive press with a omial power of 25 N (2,5 t). Our methods were quite simple. We prepared parameters of commo 25 N forgig press ad the we made desig calculatios for its drive. At the ed of this paper we tried to discus eergy efficiecy which should be better for direct drive (accordig to producers proclamatios). 2. Forgig press 25 N [], [2], [3] Before creatig a specific techical assigmet we made market research, where we focused o curret ad historical forgig presses with a omial force of 25 N. Followig parameters arose from the survey: Nomial force Stroke Cotiuous operatio at Ram stroke Press shut Coectig rod legth otor power (flywheel) 25 N 25 mi- 6 mi- 35 mm 95 mm 275 mm 3 kw For the purpose of determiig the size of the drive we came out of the press SCHULER PK 6 SDT. There is cosidered omial agle α j = 2 ad rectagular shape of deformatio characteristics (see Fig. ). Rated agle correspods to the useful stroke h u = 2 mm. F j F [N] hu A u rectagular h [mm] Fig.. Rectagular shape of deformatio characteristic. Useful work equal to: 25N 2mm kj () Au F j hu aximum torque at eccetric shaft To esure omial force with a certai reserve (for example eeded for frictio loses) it is cosidered force overload of 2% which correspods to the force F AX = 3 N.

3 6 Ja Hlaváč ad ila Čechura / Procedia Egieerig (25 ) Torqu o the eccetric shaft [knm] knm at Work force [N] 6, 65, 7, 75, 8, agle of rotatio from top DC [ ] Torque Force Fig. 2. Progress of work force ad eeded torque. For derivig of the required maximum force is to eeded to act torque max = 227 knm with the eccetric shaft. Cocrete progress is show i the previous figure (Fig. 2). Specified torque does ot affect losses caused by frictio betwee the eccetric shaft ad puttig it i the machie frame Choice of drive motor The followig proposal is made for two egies OSWALD TF36.2, whose parameters are as follows (Fig. 3): Number of motors = 2 pcs Nomial power oe motor P = 54 kw Istalled power P _istal =,8 kw Nomial speed = 5 mi- The omial torque = 9.6 knm The maximum torque max = 27 knm aximum speed F = 75 mi- aximum mechaical speed max = mi- otor overload p =.5 otor weight m = 75 kg If we cosider the operatio of egie with a overload, the maximum torque max reached at egie speed: max 6 p PN 6, ,4 mi max (2) To achieve the required torque max eeded to iduce omial force there is eed to use trasfer with ratio:

4 Ja Hlaváč ad ila Čechura / Procedia Egieerig (25 ) i AX max , (3) At maximum motor speed eccetric shaft will rotate at speeds: AX i F 75 9,98 mi 37,55 (4) At maximum motor speed with o overload F there is available motor torque (both egies): 6 P N F 2, 8 F 2 75 knm (5) Eccetric shaft rotate speed correspodig to the maximum torque with overload is: IN i max, , mi 37,55 (6) omet at maximum speed with overload coverted to eccetric shaft has a value of: 2 F i p 22,8 37,55,5 44, knm (7) F 9 Previous calculatios are summarized i the followig chart (Fig. 3) Eccetric shaft torque [knm] regio of variable speed - 5 costat power The agle of rotatio from TDC [deg] Eccetric shaft speed] AX = 2 27 knm IN = 7,2 mi - AN = 9,98 mi - Eccetric shaft speed Eccetric shaft speed [mi-] Fig. 3. Display of progressio of the speed of eccetric shaft ad of eccetric shaft torque depedig o the positio of the ram.

5 62 Ja Hlaváč ad ila Čechura / Procedia Egieerig (25 ) Determiatio of the time oe revolutio of eccetric shaft Time oe revolutio of eccetric shaft is built o the assumptio that the motor rotates i its maximum speed F = 75 mi -. Whe applyig techological operatios will spi their maximum speed or the speed correspodig to the istalled capacity (determied from the momet of overloaded motor). Time calculatio is performed for the maximum force F AX = 3 N. This icreased load covers the existece, ot cosidered i the calculatio, of passive resistace i the crak mechaism ad power efficiecy of trasmissio gearig. Torque at the eccetric shaft is i the rage of 6 to 73 higher tha torque at the maximum speed F. I this rage maximum egie power with overload will be used - speed will decrease to IN. Time for oe revolutio of give assumptios is: t F _ AX 3, s (8) This correspods to the umber of strokes per miute: oper t 6 6 9,3 mi 3, F _ AX (9) 35 3 Ram possitio [mm] ,2,4,6,8,2,4,6,8 2 2,2 2,4 2,6 2,8 3 Time [s] specific ram speed costat speed Fig. 4. Display positio of the ram i relatio to time for a specific stroke ad uiform stroke at costat speed (from the graph it is clear that durig the formig of reducig movemet speed). Figure (Fig. 4) shows the time depedece of the specific ram stroke (solid lie). Steady stroke (show for the same time speed; dashed lie) shows a situatio where the eccetric shaft rotatio speed costat. For a specific stroke it is evidet that the ram moves i its idle portio faster, but i areas where there is a formig operatio (bottom dead ceter) its speed decreases.

6 Ja Hlaváč ad ila Čechura / Procedia Egieerig (25 ) Pedulum mode Pedulum mode, for example, cosists of limitig the rotatio of the eccetric shaft i positio 9 before ad 9 after BDC (9-27 absolute), which always stops the drive ad the chage the sese of rotatio. Whe cosiderig the istat stop ad istat start back, time of oe stroke is: t pedulum, 6 s () After that, the umber of strokes is: oper t ,5 mi,6 pedulum () 2.5. Trasmissio Although it is a direct drive, which is usually see as a direct coectio with motor-drive compoet without the eed for a trasfer, if the crak forgig press with a additioal a trasfer is uavoidable. Desired speed eccetric shafts are too low eve for low-speed drives, such as torque motors. I the previous text it is cosidered a pair of drive torque motors OSWALD TF36.2 whose omial speed is 5 mi-, therefore trasfer ratio is eeded to determie the required speed. From OSWALD motors could be used eve slower oes, specifically OSWALD TF62.8 whose omial speed is 2 mi - ad performace is similar to the proposed motor. Low speed is redeemed by its higher weight, amely a motor OSWALD TF36.2 weighs,75 kg ad motor OSWALD TF62.8 weighs 3,55 kg, so the choice, despite the eed for greater trasfer it is relatively easy. For such a large trasfers shall be used a plaetary gear, the coectios could be as follows, see Fig Eergy maagemet Fig. 5. Coectio diagram of direct drive with plaetary gear to eccetric shaft of press. [4], [5], [6], [7], [8], [9] Direct drive cosumes eergy i depedece o the actual system requiremets, ad sice it is ot a small eergy the torque motor caot be coected directly to distributio etwork. Betwee the torque motor ad the power grid must be iserted electricity storage device. ethods of accumulatio of electrical eergy are several. Basic priciples are two, which are further divided (selectio): Chemical priciples - Lead-acid, alkali ad other (Li-Io,...) batteries

7 64 Ja Hlaváč ad ila Čechura / Procedia Egieerig (25 ) Supercapacitors The physical priciples - Flywheels - Pumped storage hydro power plat - Eergy storage based o compressed air For the purpose of mechaical drive of the press it is essetial to esure a adequate eergy supply (i this case, mi. 3 kj) ad to esure the possibility of rapid loadig ad uloadig of the accumulator (i the order of. s). Ad of course there is a coditio o the spatial low demads. Usable storages are supercapacitors or the flywheel of the listed methods of accumulatio. The use the flywheel is essetially oly a move of flywheel of covetioal drive out of the machie. Yes, that will remove the couplig (eergy loss) from the system, but this is compesated by the ecessity of use of two powerful motor / geerators whe oe is coected to the eccetric shaft ad the secod to the flywheel. The power trasmissio will always be dissipatio. 3.. System efficiecy Oe of the advatages of direct drive is its higher efficiecy (lower eergy loss). It is because of the remove of the clutch ad brake ad vice versa eergy recovery is used. But there is o specific compariso. It does ot exist or is ot available publicly. Some ideas of the efficiecy of the drive is i creatio based o the descriptio of actuators, i.e. what happes betwee eergy grid ad eccetric shaft Loses i covetioal drive Covetioal drive cosists of a asychroous motor (for 25 N forgig press it is about 5 kw), which ca be powered via a frequecy coverter. The efficiecy of such a motor varies aroud 92% depedig o the speed [7]. The actual efficiecy of coverters ca be up to 98%. V-belt trasmissio with the efficiecy approximately 96% [4] is used o the press. Flywheel itself it is located o a separate shaft which is supported by roller bearigs, whose efficiecy is reported to be about 99%. Follow trasfer gears whose efficacy is at least 98%. The ext member it is drive clutch. The clutch is a place where there are sigificat eergy losses of the slip at closig. Because the size of the loss depeds o may parameters, it caot be simply expressed as a specific percetage efficacy. Similarly to couplig it is difficult to describe brake that stops the movig mechaism at TDC Loses i direct drive Direct drive cosists of a special torque motor which idicated efficiecy at rated speed ad power is about 96% [3]. But efficiecy will be lower at other tha rated speed. The motor is powered via cotrol uit which cosists of voltage coverters ad rectifiers whose efficiecy is about 98% ad 99%. There are used trasfer gears ad plaetary gear with efficiecy 98% ad 97% [5]. The drive itself is therefore more efficiet. But whe there must be added the ifluece of eergy storage, the overall efficiecy will be lower. I the case of use of the supercapacitors it is ecessary to cout with their life of about millio cycles of charge ad discharge efficiecy i the rage of 88-98%. Accumulatio i the flywheel is associated with the deploymet of aother powerful motor / geerator with the ecessity of cosiderig the effectiveess of its cotrol electroics as well as at discharge ad durig chargig. Ad the lie resistace losses are ot egligible too. Sufficietly powerful flywheels are commercially available, bigger commercially used flywheel provides aroud,6w for s [6]. The overall efficiecy of such a drive is also ot too high.

8 Ja Hlaváč ad ila Čechura / Procedia Egieerig (25 ) Coclusio The purpose of this paper is to desig the direct drive of the forgig press with a omial force of 25 N. The impulse for the very existece of the solutio was 6 N forgig press with direct drive produced by SCHULER GROUP. Withi the program of our Cetre CVTS where we deal with desig of formig machies we have decided to desig larger machie 25 N forgig press with direct drive. The result of our efforts is a rough draft of a possible of direct drive. I our proposal we used may simplificatios, such as the crak mechaism do ot cosider passive resistace, but o the other had, we cosider a rectagular deformatio characteristics from 2 before bottom dead ceter ad possible force overload. We do cosider our proposal to be real. The result is that it is possible to produce such a powerful press. We igored detail proposal of plaetary gear, which certaily affects the productio cost of the machie, or a particular way of accumulatio of electric eergy, which also affects the fiacial aspect, but also the spatial requiremets of the ew press. We are tryig to ope a discussio about eergy efficiecy of both drive ways. There are too may beefits metioed by direct drive machies producers but there is o real compariso. This Article shall ot discuss the reported techological advatages of direct drive (about which we ca doubt), or we do ot attempt to compare the fiacial performace of a particular solutio, but we oly outlies the specific solutio for a medium to large forgig presses. Ackowledgemets This work was partially supported by iteral grat of Uiversity of West Bohemia i Pilse SGS-23-5 ad partially by TE275 - Competece Ceter - aufacturig Techology grat of Techology Agecy of the Czech Republic (TA ČR). Refereces [] J. Hlavac,. Cechura, J. Staek. Direct drive i formig machi desig (Origial title: Přímý poho v kostrukci tvářecích strojů). Kovarestvi. 22, 44, s ISSN [2] SCHULER GROUP. New 6,-kN Drop Forgig Press. Forgig [olie]. 24 [cit ]. Accessible: [3] OSWALD ELEKTROOTOREN GBH. Torquemotore: Drehstrom-Sychro-otore. OSWALD [olie]. 23 [cit ]. Accessible: [4] TYA CZ, s.r.o.. Belt drive efficiecy ad its improvemets (Origial title: Účiost řemeových převodů a její zvýšeí). TYA [olie] [cit ]. Accessible: [5] Secodary Techical School of Egieerig. Geared trasmitios (Origial title: Ozubeé převody). SPSSOL [olie]. [cit ]. Accessible: [6] P. Dvorak, P. Baca, D. Pleha. Electricity accumulatio (Origial title: Akumulace elektřiy). TZB-ifo [olie] [cit ]. Accessible: [7] SIEENS. ai motors. Siemes AG [olie]. 2 [cit ]. Accessible: [8] J. Jeicek, P. Polcar. Supercapacitors chargig ad dischargig (Origial title: Nabíjeí a vybíjeí superkapacitorů). Plze, 22. Bachelor thessis. UWB Plze, Faculty of Electrical Egieerig, Departmet of Applied Electroics ad Telecommuicatios, 22. Accessible: [9] SIEENS. icromaster 42/43/44 Iveters.2 kw to 25 kw. Siemes AG [olie]. 27 [cit ]. Accessible: