© Strojni{ki vestnik 48(2002)5,283-294 © Journal of Mechanical Engineering 48(2002)5,283-294 ISSN 0039-2480 ISSN 0039-2480 UDK 62-25:621.983.4:621.753.5 UDC 62-25:621.983.4:621.753.5 Pregledni znanstveni ~lanek (1.02) Review scientific paper (1.02) Prispevek k obvladovanju neuravnote`enosti krempljastih polov alternatorjev A Contribution to the Unbalance Control of Claw Poles for Automotive Alternators Miha Nastran - Vid Kru{i~ - Miha Bolte`ar Krempljasti poli so se vedno največji in najtežji sestavni del rotorja alternatorjev, ki bo vsaj se nekaj časa ustvarjal električno energijo v motornih vozilih. Zaradi visokih vrtljajev, ki jih alternator med delovanjem doseže, je masna uravnoteženost rotorja bistvenega pomena za dobo trajanja ležajev, majhen hrup in miren tek Prispevek obravnava izdelavo krempljastih polov s hladnim preoblikovanjem, pri čemer je poudarek na zmanjšanju njihove neuravnoteženosti, s čimer bi bistveno pripomogli k pospešitvi avtomatskega uravnoteženja rotorjev. V začetku je na kratko orisan problem ter samo načelo uravnoteženja. V nadaljevnju sledi eksperimentalna analiza sedanje proizvodnje, z uporabo metode končnih elementov pa razložimo vzroke za pojav neuravnoteženosti. Poudarek je dan raziskavam v smeri izboljšav sedanjega orodnega sistema za doseganje majhne neuravnoteženosti krempljastih polov. © 2002 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: rotorji alternatorjev, uravnoteženost mas, sistemi orodni, metode numerične) The claw pole still represents the largest and the heaviest part of an alternator’s rotor; and it is expected that alternators will continue to be used for electric power generation in motor vehicles for at least a decade. Due to the high speeds of the rotor during operation its mass centricity is very important for the service life of the bearings, low noise and smooth running. This paper presents the production of claw poles using cold-forming technology, and a focus on reducing the eccentricity. Achieving this aim will mean a step towards shortening the time needed for automated balancing. We start with the problem of production and principle of balancing, this is followed by an experimental analysis of current production and a FEM analysis, which helps to describe the reasons why unbalance occurs. Emphasis is placed on work towards improving the tooling system for achieving well-balanced claw poles after cold forming. © 2002 Journal of Mechanical Engineering. All rights reserved. (Keywords: alternator rotors, mass centricity, tool systems, numerical methods) 0 UVOD Geometrijska natančnost polizdelkov je še vedno eden glavnih problemov v tehnologiji hladnega preoblikovanja. Pri tem ima pomembno vlogo preoblikovalno orodje, ki s svojimi značilnostmi prispeva h kakovosti izdelka [1]. Način, s katerim se rešuje problem merske nenatančnosti polizdelkov, je navadno odvisen od geometrijskih značilnosti polizdelka. Zmanjšanja preoblikovalnega odpora z načelom sprostitvenih osi na mestih z največjo napetostjo se je lotil že Kondo ([2] do [4]). Podobna metoda je bila uporabljena tudi za hladno kovanje zobnikov ([5] in [6]). V prispevku je prikazan problem natančne izdelave krempljastega pola s hladnim preoblikovanjem (sl.1) ter podane smernice za ustrezne poprave orodja. 0 INTRODUCTION The geometrical accuracy of products is still one of the major problems facing cold-forming technology. The forming tool and its characteristics have an important affect on the quality of the finished part [1]. The principle used for controlling geometrical errors depends mainly on the geometrical properties of the product being produced. Lowering the forming resistance by the principle of relief axis at the points with the highest pressure is one of the methods that has been used already by Kondo ([2] to [4]). A similar method has been used in the cold forming of gears ([5] and [6]). The problem of geometrically accurate production of the claw pole by using cold-forming technology is presented in the paper (Fig.1), and some advice relating too an improved forming tool is given. gfin^OtJJIMISCSD 02-5 stran 283 |^BSSITIMIGC Nastran M. - Kru{i~ V. - Bolte`ar M.: Prispevek k obvladovanju - A Contribution to the Unbalance Sl. 1. Platina in izdelani krempljasti pol alternatorja Fig. 1. Blank and finished claw pole for alternators Med obratovanjem doseže rotor alternatorja do 18.000 vrtljajev v minuti. Ena bistvenih zahtev, ki jih je treba izpolnjevati, je majhna masna neuravnoteženost celotnega sklopa rotorja. Problem se rešuje z uravnoteženjem rotorja pred vgradnjo v celoten sklop alternatorja. V proizvodnji se to navadno doseže z odvzemanjem materiala v dveh ravninah kar je lahko v primeru velike neuravnoteženosti zelo zamuden proces. Zaradi slabih sestavnih delov se lahko zgodi, da rotorja ni mogoče primerno uravnotežiti in postane izmet. Na tem mestu se pojavi težnja po čimbolj natančno izdelanih polizdelkih (v prikazanem primeru je to krempljasti pol), ki so sestavni del končnega izdelka. 120 gmm 100 During operation the rotor of an alternator is moving at high speeds (up to 18,000 rpm), thus one of the important demands is to keep the rotor unbalance as low as possible. Balancing the rotor before its final assembly into the alternator solves the problem. In the production this is normally achieved by drilling holes in two planes, which is often a time-consuming process if the rotor is very unbalanced. In some cases it is impossible to achieve the prescribed tolerance. Thus the need for the cold-formed parts, in this case the claw pole, to be as precise as possible is clear. 80 60 40 20 0 1 11 16 21 26 št. vzorca sample number 31 36 41 46 51 Sl. 2. Meritve masne neuravnoteženosti krempljastega pola na 50 vzorcih Fig. 2. Unbalance measurements of the claw pole for 50 samples Krempljasti pol je najtežji sestavni del rotorja, zato se je primerno posvetiti njegovi izdelavi v smeri majhne neuravnoteženosti. Analiza trenutnega stanja v proizvodnji krempljastih polov pokaže na veliko neuravnoteženost (sl.2), saj merjeni rezultati presegajo dovoljeno mejo 80 gmm (velikost se navadno podaja v gmm, kar pomeni določeno maso materiala na določeni ročici). Zmanjšanje masne neuravnoteženosti krempljastih polov je zato eno ključnih vprašanj. 1 NAMEN URAVNOTEŽENJA Uravnoteženje delimo na uravnoteženje togih ter prožnih rotorjev ([7] in [8]). Pri prožnih rotorjih The claw pole is the heaviest part of the rotor so it is worth spending time to reduce its unbalance. An analysis of the current production shows a large degree of unbalance (Fig.2). The measured values exceed the upper limit of 80 gmm, (it is normally measured in gmm which represents a certain amount of material on a given radius). Reducing this unbalance is therefore one of the main tasks. 1 THE PURPOSE OF BALANCING Balancing is basically divided onto the balancing of rigid and elastic rotors ([7] and [8]). VH^tTPsDDIK stran 284 6 Nastran M. - Kru{i~ V. - Bolte`ar M.: Prispevek k obvladovanju - A Contribution to the Unbalance moramo izvajati modalno uravnoteženje, pri katerem je treba upoštevati upogibne deformacije gredi. S tem se v našem prispevku ne bomo ukvarjali. Pri uravnoteženju togih rotorjev poznamo uravnoteženje v eni (statično) in več (dinamično) ravninah. Pri uravnoteženju v eni ravnini za počasi tekoče rotorje poskušamo odpraviti njihovo izsrednost oz. uravnotežiti momente mase. Pri balansiranju v dveh ali več ravninah pri hitrotekočih rotorjih pa poskušamo odpraviti masne deviacijske momente glede na par pravokotnih osi, od katerih je ena vedno os vrtenja. Z drugimi besedami, želimo odpraviti momente centrifugalnih sil pri vrtenju. Uravnoteženje se lahko izvaja terensko, pri čemer se rotor vrti v svojih ležajih, ali pa na uravnotežnih napravah, kjer rotor namestimo na napravo ter ga testno zavrtimo za ugotovitev neuravnoteženosti. Slednja možnost se uporablja tudi pri velikoserijski izdelavi alternatorjev na avtomatiziranih balansirnih napravah Kupci alternatorjev predpisujejo največjo masno neuravnoteženost, ki jo morajo rotorji dosegati. Pri uravnotežanju z odvzemanjem materiala, ki je v navadi pri množični proizvodnji rotorjev alternatorjev, se pojavijo omejitve pri možni količini odvzetega materiala. Preveliko odvzemanje lahko povzroči celo dodatne neprijetne učinke, npr. pojav magnetne neuravnoteženosti pri uravnoteženju rotorjev elektromotorjev [9]. Ker namen prispevka ni poglobljeno obravnavanje uravnotežnega sistema temveč raziskava možnosti za izboljšanje polizdelkov, bomo v nadaljevanju predstavili tehnološki postopek izdelave krempljastega pola. 2 TEHNOLOŠKI POSTOPEK IZDELAVE Izhodiščni material za izdelavo krempljastega pola s hladnim preoblikovanjem je debela pločevina, navita na kolute, iz katere se najprej izsekajo platine v obliki zvezd (sl.1). Debelina platin je odvisna od tipa krempljastega pola in se giblje med 10 in 13 mm. Sledi hladno preoblikovanje v sedmih stopnjah na prenosnem orodju, pri čemer se postopoma pride do končne oblike. Po hladnem preoblikovanju sledi še žarjenje za izboljšanje magnetnih lastnosti materiala. Z vidika masne neuravnoteženosti izdelanega krempljastega pola je zlasti pomembna prva operacija na prenosnem orodju, ko se s tehnologijo finega reza prebije luknja. Centriranje platine v prvi stopnji je prikazano na sliki 3. Funkcionalno je luknja namenjena pritrditvi pola na gred rotorja, med postopkom izdelave v naslednjih šestih stopnjah orodja pa je uporabljena za pozicioniranje platine v orodju. Centričnost izdelane luknje glede na pozicionirne trne je 0,032 mm, to pomeni, da bi v primeru popolnoma geometrijsko pravilno izdelane platine masna neuravnoteženost izdelanega krempljastega pola nihala za ± 13 gmm. V primerjavi s skupno izsrednostjo Modal balancing is necessary for elastic rotors, where bending deformations of the shaft need to be taken into account. This topic will not be discussed in the paper. Single-plane (static) and multiplane (dynamic) balancing are used with rigid rotors. Single-plane balancing is needed for slow-running rotors where gravity moments need to be eliminated. During dynamic balancing the aim is to reduce the massdeviation moments with regard to two perpendicular axes, one of which is the axis of revolution. In other words, the centrifugal moments during rotating should be removed. Two different balancing principles are used in practise. The first case is when the rotor is rotating in his own bearings. In the second case, special balancing machinery is used to test and correct the rotor. This latter method is also used in the mass production of alternators. The highest mass unbalance of the rotors is prescribed by the customer. The balancing principle in mass production normally involves removal of the material by drilling. There are certain limitations relating to the amount of material that can be removed. If too much material has to be removed in order to keep the rotor in the tolerance field some other effects can appear. For example, magnetic unbalance during the balancing of rotors for electric motors [9]. The aim of our paper is not to discuss the theoretical principle of balancing but to improve the mass balance of a cold-formed claw pole. Therefore, the technological process of claw-pole production will be presented in the next section. 2 TECHNOLOGICAL PROCESS The material used for claw-pole production in cold-forming technology is thick sheet metal bound in coils. Blanks are made first by free blanking. The thickness depends on the type of claw pole and ranges between 10 and 13 mm. Next, the blanks are formed to their final shape on a mechanical press using a seven-step transfer die. Finally, the claw poles are annealed to improve their magnetic properties. Flow piercing of the hole (first transfer die) is a forming step that has a major affect on the final claw-pole unbalance. Positioning of the blank in the first transfer die is shown in Fig.3. The hole is used for mounting the claw pole onto the rotor shaft. It is also used for positioning the blank during forming in subsequent operations. The manufacturing tolerance field of the piercing punch with regard to the positioning pins is 0.032 mm. If the blanks were produced in a geometrically precise way, the maximum theoretical unbalance would be 13 gmm. This is a negligable | lgfinHi(s)bJ][M]lfi[j;?n 02-5______ stran 285 I^BSSIfTMlGC Nastran M. - K nbalance platina - blank pozicionirni trn -positioning pin matrica - die izdelanega krempljastega pola je to zanemarljivo, saj se ta giblje pri vrednosti 80 gmm. Iz povedanega smemo za neuravnotežje izdelanih krempljastih polov sumiti prvo tehnološko operacijo (prosto rezanje), pri kateri ne izdelamo geometrijsko pravilne oblike platine. Ta nepravilna oblika je bistvena za vnos neuravnotežja v polizdelek, ki se nato prenese v končni izdelek. 3 VZROKI ZA NASTANEK NEURAVNOTEŽJA PRI PROSTEM REZANJU Želja po čim boljšem izkoristku materiala narekuje čim gostejšo postavitev platin na trak. Izkazalo se je, da je le to ključnega pomena za nastanek masne neuravnoteženosti. Z namenom, da bi ugotovili vpliv velikosti mostička med dvema platinama, smo dva pestiča vzeli iz orodja in povečevali razmik izrezanih platin. Rezultati so prikazani na sliki 4, kjer se vidi, da se je ob večanju razmika med platinama masna neuravnoteženost izdelanega krempljastega pola zmanjšala. Glavni vzrok za izsrednost izdelanega krempljastega pola je izsredena obremenitev stiskalnice in nesimetričen rez, ki je posledica neenakomerne porazdelitve materiala okrog rezilnega pestiča. Pri gibu orodja navzdol nastanejo poleg glavne rezalne sile v smeri giba orodja še stranske rezalne sile, ki pa med seboj niso v ravnotežju (sl.8). 120 -^^ r\ 100 \> V 80 '") J) j 60 amount compared to the total claw-pole unbalance, which is around 80 gmm. Therefore, we can conclude that the first operation, the free blanking of the blanks, is essential for the accuracy of the finished product, where a geometrically imperfect blank is made. This nonsymmetrical geometry of the blank is essential for the unbalance of the finished product. 3 REASONS FOR NONSYMMETRICAL FREE BLANKING In order to save on the material costs it is necessary to arrange the blanks to be as close together as possible. However, many problems occur for this reason, a fact that was experimentally verified. In order to determine the influence of the web width, two punches were taken out of the tool and the feed was increased. The results are presented in Fig.4. We can conclude that when the web width is increased the unbalance of the finished claw pole becomes proportionally lower. The major reason for the unbalance of the finished claw pole is a non-symmetrical blanking, which is the reason for the nonuniform distribution of the material surrounding the blanking punch. Apart from the major blanking force there are side forces that emerge when the tool closes (Fig.8). These side forces are not symmetrical due to V/ ^ ( T TI 115 r / 13 148 40 -/- 0 V^t 1 3 5 7 9 11 št.vzorca sample num. 13 15 pomik - feed [mm] 115 -•----133 ¦ ±--163 Sl. 4. Vpliv razmika platin na izsredenost Fig. 4. Influence of the blank scatter on the eccentricity VH^tTPsDDIK stran 286 Nastran M. - Kru{i~ V. - Bolte`ar M.: Prispevek k obvladovanju - A Contribution to the Unbalance pomik navzdol - punch travel stranski premik - side displacement Fig. 5. Horizontal shift of the punch relative to the die Zaradi zračnosti v vodilih orodja in stiskalnice povzročajo stranski premik pestiča v primerjavi z matrico (sl.5). Za potrditev domneve o pojavu nesimetričnih stranskih sil na pestič med postopkom rezanja je bilo narejeno numerično simuliranje začetne faze rezanja. Skušali smo napovedati dogajanje po obodu enega zoba pestiča. Problem je v tem, da je zaradi poprej izrezane platine na eni strani zoba pestiča bistveno več materiala kakor na drugi strani (sl. 8). Posledica tega je razvoj bočnih sil na zob pestiča, ki nista v medsebojnem ravnovesju in povzročata vodoravni premik pestiča. Z dvema numeričnima simuliranjima začetne faze rezanja, pri čemer je bilo v prvem primeru okoli pestiča manj materiala v drugem pa več, smo domnevo potrdili (sl. 6 in 7). Primerjava deformacij platine v obeh primerih pokaže, da ima v primeru, ko je na zunanji the different size of the web. Because of the clearing in the tool and press guiding system these side forces cause a punch shift relative to the die (Fig. 5). In order to confirm our assumption about the development of side forces on the punch we made a numerical simulation of the beginning of the cutting process. The circumstances on one side of the blanking teeth were predicted. The problem is a nonuniform distribution of the material surrounding the punch, due to the blank cut in the previous step (Fig. 8). A consequence is the development of side forces on the punch, which causes a horizontal shift of the punch. The assumption was confirmed by performing two numerical simulations of the initial cutting phase. In the first case less material was used surrounding the punch, in the second case more material was used (Fig. 6 and 7). Comparing the deformation in the first a) b) Sl. 6. Model zoba pri rezanju platine a) manj materiala b) več materiala Fig. 6. FE Model during blanking a) less material b) more material | IgfinHŽslbJlIMlIgiCšD I stran 287 glTMDDC Nastran M. - Kru{i~ V. - Bolte`ar M.: Prispevek k obvladovanju - A Contribution to the Unbalance strani pestiča manj materiala, le-ta veliko večjo težnjo po gibanju navzgor in s tem proti pestiču. Deformacija zgornjega dela platine je v prvem primeru 0,045mm v drugem pa 0,01mm. Prav tako je potrjena domneva o neenakomernem razvoju prečnih sil na pestič, kar ima za posledico pritiskanje zoba pestiča v stran. Potek sil v ravnini pestiča je prikazan na sliki 8. V primeru večje količine materiala na zunanji strani pestiča je bočna pritisna sila manjša. Komponenta sile v smeri zoba zaradi deformacije ni problematična, ker je po obodu celotnega pestiča nameščenih šest zob, katerih sile se med seboj izničijo. Problematična je rezultanta sile prečno na zob, katere velikost je glede na rezultate simuliranja približno 1,5 % celotne preoblikovalne sile. Z upoštevanjem dejstva, da je potrebna sila za rezanje ene platine 2000 kN, pomeni to 27 kN bočne sile na zobe, ki povzročajo torzijo pestiča in s tem neenakomeren potek kota lomne cone na platini. Odpravljati vzroke premika rezalnih pestičev na orodju in stiskalnici bi bilo ekonomsko neupravičeno, saj bi pomenilo bistvene posege v stroj in orodje. Povečanje and second case shows that when there is less material near the punch it has a much higher tendency to move upwards and towards the punch. Vertical deformation of the blank in the first case is 0.045 mm, and in the second case it is 0.01 mm. The assumption of the nonsymmetrical side forces was confirmed as well, these forces cause a sideways movement of the punch. The forces acting on the punch are presented in Fig. 8. In the case when we have more material outside the punch the side force is lower than with less material. The force component acting parallel to the punch tooth is not problematic since there are six teeth arranged circumferentially and the forces disappear. The most problematic component acts perpendicularly to the tooth. Its magnitude is 1.5% of the total blanking force, according to the simulation. Taking the 2000 kN that is needed for one blank into account, it means 27 kN of side force. These forces are the reason for the torsional punch displacement, which causes a nonuniform distribution of the angle of the fracture zone. Solving the problem of the horizontal punch displacement would mean large investments in the tool and press, which may not be the correct economic decision. Increasing the web width between the blanks Sl. 7. Deformacija platine v prvem in drugem primeru Fig. 7. Blank deformation in the first and second cases 4 3,5 3 2,5 2 1,5 1 0,5 0 -0,5 -1 -1,5 -2 -2,5 -3 * F2x 1x F2y F 1y -----a več materiala more material manj materiala less material 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 pomik pestiča - punch travel [mm] -x F2y Sl. 8. Komponenti rezalne sile na pestič v ravnini platine Fig. 8. Blanking force components in the blank plane VH^tTPsDDIK stran 288 1 Nastran M. - Kru{i~ V. - Bolte`ar M.: Prispevek k obvladovanju - A Contribution to the Unbalance razmika med pestiči pa bi hkrati pomenilo tudi manjši izkoristek materiala ter povsem novo orodje za rezanje. Zaradi povedanega se bomo osredotočili na prvo operacijo v prenosnem orodju - fino rezanje luknje. 4 TEORETIČEN IZRAČUN NEURAVNOTEŽENOSTI Da bi potrdili domnevo o glavnem vplivu nesimetričnega odreza platine na masno neuravnoteženost izdelanega krempljastega pola, je bila masna neuravnoteženost tudi teoretično izračunana na podlagi meritev premika pestiča pri rezanju platin. V primeru morebitnega ujemanja izračunanih rezultatov ter rezultatov meritev neuravnotežja izdelanega krempljastega pola, je jasno, da preoblikovanje na prenosnem orodju ne vpliva bistveno na končno neuravnoteženost izdelka. V ta namen je bilo iz serije vzetih 25 platin, na katerih smo merili kot preloma materiala med rezanjem (sl. 9). would mean higher material costs, which is again not a profitable solution. Apart from that, a completely new blanking tool will be required. Because of this, further discussion will be focused on the flow piercing of the hole, which is the first operation in the transfer die. 4 THEORETICAL CALCULATION OF THE ECCENTRICITY In order to confirm the assumption about the major affect of the blanking tool on the claw-pole unbalance we made a theoretical calculation of the unbalance. It was based on the punch shift during blanking, which was measured by examining the blanks. When the results obtained theoretically by inspecting the blanks are identical to those measured on the finished claw poles we can conclude that the forming on the transfer tool does not have any affect on the overall unbalance. In order to perform this calculation, 25 blanks were taken from production. The angle of the fracture zone was measured at six positions on the blank (Fig.9). mesta meritve kota preloma measuring point of the cut inclination Sl. 9. Meritev kota preloma materiala na platini Fig. 9. Measuring the cutting angle on the blank Iz šestih meritev kota preloma materiala sta bili The direction and amplitude of the punch shift ocenjeni smer ter velikost premika pestiča proti matrici, were calculated based on six measurements of the iz tega pa izračunana masna neuravnoteženost platine: angle, the theoretical unbalance was also calculated: D0 = t- D60 = t- D= 120 t- j +j tan 0 180 - tanj0 j +j tan 60 240 - tanj60 (1). j +j tan 120 300 - tanj120 1 gfin^OtJJIMISCSD 02-5 stran 289 |^BSSITIMIGC ce 60° 120° Sl. 10. Izračun premika pestiča proti matrici Fig. 10. Calculation of the punch shift Oznake v enačbah so glede na sliko 9: ji - kot preloma pri kotu i v vodoravni ravnini v °, t - debelina lomne cone v mm, A -velikost premika pestiča v smeri i v vodoravni i ravnini v mm. Zaradi napak pri merjenju pa je rezultanto premika primerno določiti po metodi najmanjših kvadratov. In Fig.9 the following notation is used: ji - fracture angle at an angle in the horizontal plane, t - fracture-zone thickness, Di - punch shift in the i-th direction in the horizontal plane [mm]. Because of the measurement errors the punch shift calculation was based on three measurements using the least-square method. G = [D-cosj-D0]2+[D-cos(j-600)-D60]2+[D-cos(j-1200)-D120]2 (2). Pri čemer je D absolutna vrednost premika pestiča, j pa smer, v kateri se premakne (sl.10). Z minimiziranjem funkcije G pridemo do končnega rezultata. V ta namen parcialno odvajamo po D in j: Where D is an absolute punch displacement, j is the displacement direction (fig.10). By minimizing the function G a final result is obtained by partial differentiation in D and j: dG dj dG d D tanj = V3(D60 + D1 2-D0 +D 3 ¦sinj 2-D •cosj (3), (4), (5). Dobljeni sta smer in velikost premaknitve pestiča, iz česar se nato po enačbi (6) izračuna še teoretična neuravnoteženost platine: Based on the direction and the amplitude of the punch shift, a theoretical unbalance of the claw pole is finally calculated according to: U Posamezne oznake so: U - masna neuravnoteženost v gmm, D - premika pestiča v mm, s - debelina materiala v mm, m - masa platine v g Na vzorčnih platinah je bila označena izračunana smer premika pestiča proti matrici, nato pa so bile prenesene v prenosno orodje, kjer je bila D t_ 2 s (6). Notation: U - eccentricity [gmm], D - punch shift [mm], s - material thickness [mm], m - blank mass [g] The calculated direction of the eccentricity of the blanks was marked before being put into the transfer die. A sample charge of claw poles was VH^tTPsDDIK stran 290 Nastran M. - Kru{i~ V. - Bolte`ar M.: Prispevek k obvladovanju - A Contribution to the Unbalance 120 100 80 60 40 20 ../ 360 300 240 180 120 60 # -----------•----------------------- • v • 0 20 40 60 80 100 120 masna neuravnoteženost (izmerjeno) unbalance (measured) [gmm] 0 60 120 180 240 300 360 kot zamaknitve pestiča (izmerjeno) punch shift direction (measured) [0] Sl. 11. Primerjava izračunov in meritev Fig. 11. Comparison between calculated and measured values izdelana končna oblika krempljastega pola. Po končani izdelavi krempljastih polov je bila na njih izmerjena končna masna neuravnoteženost ter smer, v kateri neuravnoteženost leži. Primerjava med izmerjenimi vrednostmi neuravnoteženosti krempljastega pola in izračunanimi vrednostmi neuravnoteženosti platin je prikazana na sliki 11. Izmerjene in izračunane vrednosti so praktično enake, kar pomeni, da je neuravnoteženost vnesena že v prvi preoblikovalni operaciji (rezanje platin). Izboljšanje rezilnega orodja je težko izvedljivo, zato bo v nadaljnjem prikazana mogoča sprememba prve stopnje prenosnega orodja (fino rezanje luknje), s čimer bi bistveno zmanjšali končno neuravnoteženost izdelka. 5 PREDLOG REŠITVE Trenutno je centriranje platine v prvi stopnji prenosnega orodja izvedeno s tremi vzmetenimi pozicionirnimi trni, medsebojno premaknjenimi za kot 1200. Prerez je prikazan na sliki 3. Problem takšne izvedbe je v tem, da je masno središče platine, kjer bi j1 produced. Afterwards a final mass unbalance and its direction was measured and compared to the theoretically obtained values. The comparison between the calculated values of the blank unbalance and the measured values of the claw-pole eccentricity is presented in Fig.11. Practically, there is no difference between the measured and the calculated values. It confirms the assumption that the eccentricity is already input at the first forming stage (blanking). Improving of the blanking tool is connected with large investments; therefore, the modification of the flow-piercing tool in the first step of the transfer die will be discussed. Much could be done in order to lower the final eccentricity. 5 SOLUTION PROPOSAL Currently, the positioning of the blank during flow piercing is made by using three positioning pins aligned in a 1200 scatter. A cross-section is presented in fig.3. The problem of this centering principle is that the mass center where the fine blanked hole should lie in j = j2 ! j2 | IgfirTHŽsIbJIlMIlgiCšD I SUMEČ 0 0 alance nevtralna ravnina neutral surface Sl. 13. Položaj nevtralne ravnine Fig. 13. Position of the neutral surface morali pozicionirati v tisti ravnini, ki v svojem središču vsebuje tudi masno središče, ta pa leži nekje med zgornjo in spodnjo površino (sl. 13). Glede na parametre platine (sl.13), ki so približno nespremenljivi, lahko lego centrirne ravnine izračunamo po enačbi (7). V enačbi se pojavljajo le stalni parametri in je torej tudi lega ravnine približno nespremenljiva. Globina prodora je predvsem odvisna od stanja orodja in je v praksi relativno nespremenljiva za vse platine (s - t ~ 4,5 mm). y =t2 e case of Due to the face does eliminate hould take place in the plane, which is symmetrical to the mass center of the blank. This plane lies somewhere between the upper and lower surface of the blank. According to the blank parameters (Fig.13), which are almost constant, the position of the centering plane can be calculated according to eq.7. The equation is based on constant parameters only; therefore, the position of the surface is constant. Punch penetration is relatively constant for all the blanks and basically depends on the tooling conditions (s - t ~ 4.5 mm). d +d ,d1-(2-s-t) + d2-t (7). Oznake: d1 - premer platine na spodnji površini v mm, d2 - premer platine na zgornji površini v mm, s - debelina platine v mm, t - debelina lomne cone platine v mm, y - oddaljenost središčne ravnine od zgornje površine platine v mm Za konkretne geometrijske parametre platine: d1 = 74,9 mm, d2 = 72,3 mm, s = 12,6 mm, t = 8,1 mm je lega nevtralne ravnine y = 5,17 mm. To pomeni, da leži v središču ploskve, ki je prerez platine in ravnine 5,17 mm pod zgornjo površino, tudi masno središče platine. Lega te ravnine je neodvisna od trenutnega premika pestiča proti matrici, kar pomeni, da jo je primerno uporabiti za usreditveno ravnino. Predlog nove izvedbe orodja je prikazan na sliki 14. Nad sedanji pozicionirni trn se namesti še drug glavni pozicionirni trn, ki bi ležal na premeru d (sl.13), kakor ga določa nevtralna ravnina: Notation: d1 - blank diameter on bottom surface [mm], d2 - blank diameter on top surface [mm], s - blank thickness [mm], t - fracture-zone thickness [mm], y - centering plane distance [mm]. For real blank parameters: d1 = 74.9 mm, d2 = 72.3 mm, s = 12.6 mm, t = 8.1 mm the position of the neutral surface is y = 5.17 mm. This means that the mass center of the blank lies in the center of the surface, which is 5.17 mm below the top surface of the blank. The most important thing is that the position of this plane is independent of the punch shift during blanking. It means that this plane could be used for better centering of the blank during flow piercing. The tool scheme of the new centering principle is presented in Fig.14. Above the current positioning pin another one (major) is mounted. The position of this pin will be determined by the diameter d (Fig.13) of the neutral plane: d =d2+ d1-d2 = 73,9 yt() (8). VBgfFMK stran 292 Nastran M. - Kru{i~ V. - Bolte`ar M.: Prispevek k obvladovanju - A Contribution to the Unbalance Med zapiranjem orodja pritisne glavni pozicionirni trn na sedanji pozicionirni trn, ki je namenjen samo za pozicioniranje v prvi stopnji, ga odmakne in s tem sprosti platino, ki se nato pozicionira glede na nov pozicionirni trn. Ta se platine dotika v prej izračunani razdalji od zgornje ravnine, ki v svojem središču vsebuje masno središče. Podlaga za takšno izvedbo pozicionirnega sistema je predvsem v tem, da je izmera matrice in pestiča med preoblikovanjem konstantna, kar je tudi praktično povsem pravilno, saj je elastična deformacija matrice in pestiča v primerjavi z deformacijo platine minimalna. Prav tako je nespremenljiva debelina materiala ter približno nespremenljiva debelina lomne cone. During the tool closing the new positioning pin acts on the current positioning pin, which is now used only for centering in the first step. It is pushed down and the blank is released for a moment and allows the upper positioning pin to position the blank in the calculated surface. It touches the blank in the previously calculated distance from the top blank surface. The basic fact for such a tool design is in first case the assumption that there is no elastic deformation of the punch and die during blanking. This is found to be correct in practice. The elastic deformation of the punch compared to the deformation of the blank can be neglected. Material thickness and the height of the punch penetration are held almost constant as well. zgornja osnovna plošča - top plate dodatni pozicionirni trn - additional positioning pin tlačna plošča - stripper pestič- punch platina - blank matrica - die sedanji pozicionirni trn - standard positioning pin naslon - spacer spodnja osnovna plošča - bottom plate Sl. 14. Načelna shema orodja Fig. 14. Tool scheme 6 SKLEP 6 CONCLUSION V prispevku je prikazano sistematično reševanje problema manjšanja masne neuravnoteženosti pri izdelavi krempljastega pola alternatorja Eksperimentalno delo in teoretična izhodišča so uspešno kombinirana in podprta z numeričnimi metodami. Poudarjen je sistematičen postopek reševanja konkretnih industrijskih problemov na področju občutljivosti in stabilnosti proizvodnih postopkov v velikoserijski proizvodnji, ki so problem tako z vidika stalnosti paramterov postopka kakor primernosti orodij [10]. Na koncu so podane še smernice za ustrezne konstrukcijske spremembe preoblikovalnega orodja, ki bi omogočal bistveno bolj stabilen tehnološki proces. A systematic approach to lowering the eccentricity of the claw poles for alternators is presented in the paper. Experimental work and theoretical aspects are combined successfully and supported with modern numerical methods. A systematic approach to solving the real industrial sensitivity and stability problems in the mass series production processes is discussed. They are problematic from the point of view of process parameters and tools [10]. Some solution proposals of constructional tool modifications for more stable and reliable production process are discussed at the end. gfin^OtJJIMISCSD 02-5 stran 293 |^BSSITIMIGC Nastran M. - Kru{i~ V. - Bolte`ar M.: Prispevek k obvladovanju - A Contribution to the Unbalance [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] 7 LITERATURA 7 REFERENCES Kuzman, K., V. Krušič (1998) Tools-one of the major attributes for the succesfull cold forging, Int. Conf. on Forging Related technologies, ImechE Conf. Trans 1998-3 333-340. Kondo, K. (1999) Improvement of product accuracy in cold die forging, Advanced Technology of Plasticity, Nueremberg, Germany,vol I, 41-48. Kuzman, K. (2001) Problems of accuracy control in cold forming. J. mater. process. technol. vol. 113, no. 1/3, special issue “5th APCMP, Seoul, Korea”, 10-15. Kuzman, K. (1999) Stability control of cold forming processes. Advanced technology of plasticity 1999: Proceedings of the 6th International Conference on Technology of Plasticity, Nuremberg, September 19- 24, Berlin [etc.]: Springer, vol. II, 805-812. Ohga, K, F.Murakoshi, HAndo, K.Miyoshi, KKondo (1999) Net shape forging of gear toothed parts utilizing divided flow method, Advanced Technology of Plasticity, Nueremberg, Germany, vol II, 793-798. Kampuš, Z., K. Kuzman (1993) Analysis of geometrical accuracy in ironing. Advanced technology and plasticity. Volume I. International Academic, 1005-1010. Kellenberger, W. (1987) Elastisches Wuchten, Springer Verlag Federn, K. (1977) Auswuchttechnik, Band1, Band 2, Springer Verlag Petrič, M. (2001) Primerjava masnega ter magnetnega neuravnoteženja rotorja z ozirom na vibracije enosmernih elektromotorjev. Fakulteta za strojništvo, Ljubljana. Gantar, G., K. Kuzman (2000) Sensitivity analysis of deep drawing production process. Proceedings of the Workshop: Characterization of Manufacturing Processes: Synergetics and Data Processing Methods, Ljubljana, May 25 - 26, 2000 , 49-53. Naslovi avtorjev: Miha Nastran doc.dr. Miha Boltežar Fakulteta za strojništvo Univerza v Ljubljani Aškerčeva 6 1000 Ljubljana miha.nastran@fs.uni-lj.si miha.boltezar@fs.uni-lj.si Vid Krušič Iskra Avtoelektrika d.d. Celovška 91 1000 Ljubljana vid.krusic@iskra-ae.com Authors’ Addresses:Miha Nastran Doc. Dr. Miha Boltežar Faculty of Mechanical Eng. University of Ljubljana Aškerčeva 6 1000 Ljubljana, Slovenia miha.nastran@fs.uni-lj.si miha.boltezar@fs.uni-lj.si Vid Krušič Iskra Avtoelektrika d.d. Celovška 91 1000 Ljubljana, Slovenia vid.krusic@iskra-ae.com Prejeto: Received: 1.2.2002 Sprejeto: Accepted: 23.5.2002 VH^tTPsDDIK stran 294