© Strojni{ki vestnik 45(1999)7/8,267-277 © Journal of Mechanical Engineering 45(1999)7/8,267-277 ISSN 0039-2480 ISSN 0039-2480 UDK 621.785.6:681.51 UDC 621.785.6:681.51 Predhodna objava (1.03) Preliminary paper (1.03) Razvoj modela procesa in strukture krmilnega sistema delovne enote za indukcijsko kaljenje The Development of a Model for the Process and Structure of a Control System for an Induction Hardening Cell Franjo Cajner - Josip Grilec - Darko Landek Da bi dosegli kakovostnejše in bolj prilagodljivo izvajanje postopka indukcijskega kaljenja, je potrebna računalniško podprta priprava in krmiljenje procesa. Prispevek opisuje in določi model procesa indukcijskega kaljenja, s katerim, ob zahtevanih parametrih postopka, dosežemo predpisano kakovost zakaljenega sloja. Nadalje obravnava vplivne dejavnike, ki opredelijo in uvajajo krmilni sistem, s katerim vodimo proces indukcijskega kaljenja v prilagodljivi delovni enoti. © 1999 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: kaljenje induktivno, modeliranje procesov, sistemi krmilni, celice fleksibilne) In order to achieve higher quality and a more flexible execution of the induction hardening process, a computer assisted program for undertaking and controlling of this process is needed. This paper proposes and describes a model for the induction hardening process, the application of which achieves a specified quality of the hardened layer, within all the parameters of the process. All the influencing factors, which define and implement the control environment used in the application of the process within the flexible working cell, are systematically analyzed. © 1999 Journal of Mechanical Engineering. All rights reserved. (Keywords: induction hardening, process modelling, control systems, flexible cell) 0 UVOD Indukcijsko kaljenje je postopek površinske toplotne obdelave, med katerim se, zaradi elektromagnetne indukcije, tanek površinski sloj na določenih površinah jeklenega obdelovanca hitro segreva do temperature avstenitizacije, nato pa se z gašenjem dosežeta želeni martenzitna mikrostruktura in trdota. S tem se zagotovi obrabna odpornost torno obremenjenih površin obdelovanca brez strukturnih sprememb v jedru obdelovanca ([1] do [3]). Da bi dosegli želene lastnosti, mora biti površinski sloj predpisane oblike, predpisana pa sta tudi globina kaljenja in površinska trdota. Pri tem ne sme priti do sprememb izmer in oblike obdelovanca. Za dosego teh zahtev je treba razviti [4]: - matematični model za optimizacijo oblike induktorjev in simuliranje procesa, - ustrezno bazo podatkov za spremljanje lastnosti materiala in delovnih karakteristik opreme, - krmilne algoritme procesa za določen material, geometrijsko obliko obdelovanca in enofrekvenčno (ali dvofrekvenčno) obdelavo, ki omogoča želeno kakovost zakaljenega sloja. 0 INTRODUCTION Induction hardening is a process by which thin surface layers, at specified areas of the steel workpiece, are heated rapidly to an austenitization temperature by electromagnetic induction, and the desired hardness and the martensitic structure is achieved by quenching. Thus, at the workpiece’s contact surfaces the wear resistance is achieved while allowing the rest of the material to be unaffected by the process ([1] to [3]). To achieve these properties the hardened surface layer has to be of a predefined shape, pre-defined depth of quench hardening and predefined surface hardness. To meet these requirements and produce quality results, it is necessary to develop [4]: - computational models for the optimal shape of inductors and for the simulation of the process, - appropriate database systems for observing the properties of the material and the working char-acteristics of the machinery, - control algorithms for the application of the pro-cess to a given material, to the geometric shape of the workpiece and to the monofrequency ( re-spectively dualfrequency ) treatment, which will result in the desired quality of the hardened layer. | gfin=i(purMini5nLn 99 stran 267 I^HSSTTIMIDC F. Cajner - J. Grilec - D. Landek V članku so prikazana načela in osnutek bodoče programske podpore projektiranju tehnologije indukcijskega kaljenja, posebej za obdelovance zahtevnejših oblik. Podan je prikaz nadzornega in diagnostičnega algoritma, ki omogoča povezavo z generatorjem, obdelovalnim sistemom, sistemom za gašenje in krmilnim sistemom za prilagodljivo delovno enoto. 1 OSNUTEK RAZVOJA PROGRAMA ZA SIMULIRANJE IN OPTIMIZACIJO INDUKCIJSKEGA KALJENJA Podatke o materialu in izmerah obdelovanca ter podatke o induktivni delovni enoti je najbolje organizirati v modularno povezane operativne in povezovalne baze podatkov. Računalniški programi, ki se uporabljajo za obdelavo tovrstnih podatkov, že obstajajo in so lahko dostopni. Za uporabo simulirnega programa indukcijskega kaljenja in programa za optimizacijo oblike induktorja so potrebne tri operativne baze podatkov: 1. baza podatkov o tehničnih značilnostih in vzdrževanju indukcijske delovne enote; 2. baza podatkov o lastnostih materiala; 3. izhodiščna tehnološka baza, tj. uspešno izvedenih in preverjenih optimizacij za posamezne materiale in obdelovance. Izvedensko znanje o procesu indukcijskega kaljenja in rešenih tehnoloških primerih je shranjeno v izhodiščni tehnološki bazi. V njo se po uspešni optimizaciji induktorja ter simuliranja indukcijskega kaljenja shranijo podatki o obliki in izmerah induktorja, parametrih segrevanja in ohlajanja ter rezultati metalografske analize preskušanca. S tem se ob vsakem reševanju problemov pri indukcijskem kaljenju razširi in poglobi znanje, kar vpliva na proces učenja in pridobivanje izkušenj. Algoritem za numerično simuliranje indukcijskega kaljenja in optimizacijo induktorja (sl. 1), je definiran na podlagi vpogleda v poročila in rezultate uporabe posameznih komercialnih in raziskovalnih simuliranj programa ([3] do [5]). Kakovost indukcijsko zakaljenega sloja -zaradi katere se izvaja simuliranje procesa in optimizacija induktorja - je definirana z obliko zakaljene cone, globino kaljenja in s površinsko trdoto. Vhodne veličine simulirnega programa morajo zbirati najpomembnejše vplive, ki odločajo o kakovosti zakaljenega sloja. Popis vplivov in njihov učinek na posamezne lastnosti sloja je prikazan v preglednici 1. Optimizacijski algoritmi, ki naj bi bili vgrajeni v omenjeni program, bodo upoštevali vplivnost navedenih dejavnikov in opozarjali uporabnika na njihovo ustrezno uporabo. 8 ^nnatäüllMliBilrSO | ^BSfirTMlliC | stran 268 This paper describes the principles and the con-cept for a future system support program for the design of induction quench hardening technology. It focuses in par-ticular on the hardening of complex shapes. Furthermore, it illustrates the control and the diagnostic algorithm that enables linking of the power supply, the workhandling system, the quenching system and the process control and monitoring system in the flexible work cell. 1 THE CONCEPT OF PROGRAM DEVELOPMENT FOR THE SIMULATION AND OPTIMI-ZATION OF INDUCTION HARDENING It is important to organize all the data relating to the material, about the dimensions of the workpiece to be treated and the induction work cell, into a modu-lar and operationally related database. Readily avail-able computer programs already exist for the design of such data. To use the induction hardening simulation program as well as the inductor shape optimizing program, three operational databases are necessary. 1. A database relating to the technical characteris-tics and maintenance of the induction work cell. 2. A database of material properties. 3. A technological initialization base, i.e. of success-fully carried out and verified optimization for single materials and workpieces. Expert knowledge about the induction harden-ing process and case by case technical solutions are stored in the technological initialization base. After successfully completing the optimizing of the inductors, and the simulation of induction hardening, the following data are then fed in to the technological base: details about the shape and the dimensions of the inductor, the heating and cool-ing parameters, and the results of the metallographic analysis of the experimental sample. Thus, with each so-lution to problems that relate to the induction hardening, the knowledge system grows and improves and acquires more elements of technical expertise. The algorithm for a numerical simulation of the induction hardening and the optimization of the inductor is defined on the basis of information received from individual research and commercial simulation programs ([3] to [5]) (Fig. 1). The quality of the induction hardened layer -the assurance of which is the reason for undertaking the simulation of the process and the optimization of the in-ductor- is defined by the shape, the depth and the surface hardness of the quench hardened zone. The initial scope of the simulation program must include the factors which most influence the quality of the quench-hardened layer. These factors and their significance with respect to individual cases are listed in Table 1. Dur-ing the development, optimizing algorithms will be in-cluded into the above mentioned program and will take into consideration the influence of the specified factors, so the user will be well informed about their adequate use. Razvoj modela krmilnega sistema - The Development of a Control System Ob začetku izvajanja simuliranja je treba določiti porazdelitev vira toplote (spremenljivo v času in prostoru) z reševanjem elektrodinamičnih enačb magnetnega polja pri podanih robnih pogojih. Postavljeni model obsega obdelovanec, induktor in zračno režo med njima. Začetna porazdelitev polja toplotnega vira pomeni vhodno spremenljivko za izračun neustaljenega temperaturnega polja in z njim povezanih faznih premen v času pregrevanja. Spremenljive fizikalne lastnosti materiala, ki so odvisne od temperature, so v modelu popisane z ustreznimi interpolacijskimi temperaturno odvisnimi zlepki, ki izhajajo iz rezultatov prejšnjih preskusov ali iz literature. Omenjena odvisnost lastnosti od temperature vnaša nelinearnost v magnetno-termodinamičen proces, kar terja iterativno izračunavanje razvite moči z uporabo numeričnih metod (npr. metodo končnih elementov, metodo robnih elementov) ([3] do [7]). At the start of the simulation procedure the heat source distribution (variable according to time and place) should be determined by solving the electro-dynamic magnetic field equations for the established boundary conditions. The corresponding model in-cludes the workpiece, the coil and the air gap. The initial distribution of heat sources rep-resents the input variable for the computation of the nonstationary temperature field and the interacting phase transformation during heating. The changeable physical properties of the material which depend on temperature are included in the model via correspond-ing spline temperature dependent functions, derived from experiments or literature sources. The depen-dence of properties on temperature produces nonlinear data in the magneto-thermal procedure, thus ne-cessitating iterative calculations of the dissipated power using numerical methods (i.e. Finite Element method, Boundary Element Method etc.) ([3] to [7]). Preglednica 1. Veličine, ki vplivajo na obliko zakaljenega sloja, globino kaljenja in potek trdot po zakaljenem sloju in jih popisujejo vhodni parametri simulacijsko optimizacijskega modela Table 1. Influencing factors on the appearance of the quench-hardened area, the depth and hardness of the hardened area included in the initial scope of the simulation optimizing model VPLIVNE VELIČINE kot VHODNI PARAMETRI MODELA INFLUENCING FACTORS as THE INITIAL SCOPE OF THE MODEL PARAMETRI, KI OPREDELJUJEJO KAKOVOST ZAKALJENEGA SLOJA CHECK MARKS OF THE QUENCH-HARDENED ZONE Oblika zakaljenega sloja Shape of the zone Oblika in izmere obdelovanca The shape and dimensions of the workpiece Kemijska sestava materiala Chemical composition of the material Toplotne lastnosti materiala obdelovanca Thermal properties of the workpiece material Električne in magnetne lastnosti materiala Electrical and magnetic properties of the material Temperatura avstenitizacije pri hitrem segrevanju Austenitizing temperature due to rapid heating Zgornja kritična hitrost gašenja Upper critical quenching speed X XX XX Poprejšnja toplotna obdelava in izhodiščna mikrostruktura Previous heat treatment and initial microstructure Postopek indukcijskega kaljenja Method of induction hardening Lega induktorja glede na obdelovanec Workpiece to induction coil location Izhodna oblika, izmere in material induktorja The initial shape, dimensions and material of the inductor Delovna frekvenca Working frequency Moč, napetost in tok induktorske tuljave Power, voltage or current of the induction coil Čas segrevanja ali premik obdelovanca Heating time or the scan speed of the workpiece Podatki o gašenju (sredstvo, temperatura, čistost in koncentracija) Quench data (media, temperature, purity, concentration) Pretok ali tlak sredstva za gašenje Flow or pressure of the quench media Koeficient toplotne prestopnosti Heat transfer coefficient____________ X Globina kaljenja Depth of hardness Trdota površine Surface hardness XX XX XX XX XX XX XX XX XX | gfin=i(purMini5nLn 99 stran 269 I^HSSTTIMIDC F. Cajner - J. Grilec - D. Landek Vnos (ali sklic na bazo podatkov) vhodnih parametrov: - geometrijski model z izmerami in pozicioniranjem obdelovanca v induktor, - robni pogoji, - fizikalne in metalurške lastnosti materiala, - parametri segrevanja in gašenja. Enter (or import from database) the initial scope: - the geometrical model with dimensions and positioning of workpiece and the inductor, - the boundary conditions, - the material physical and metallurgical properties, - the parameters of heating and quenching. INICIALIZACIJA: - izračunavanje elektromagnetnega polja, - izračunavanje toplotnih virov, - postavitev začetnega prostorskega in časovnega koraka. INITIALIZATION: - computation of the electromagnetic field, - computation of the heat sources, - initial spatial and time increments. BAZA PODATKOV o: 1. INDUKCIJSKI DELOVNI ENOTI 2. OBDELOVANCIH in MATERIALIH 3. TEHNOLOŠKIH PODATKIH DATABASE about: 1. The INDUCTION WORK CELL 2 The WORKPIECES and MATERIALS 3. TECHNICAL RECORDS MAGNETNOTERMODINAMIČNA ANALIZA (nelinearni problem) MAGNETO-THERMODYNAMIC ANALYSIS (nonlinear problem) TERMOMIKROSTRUKTURNA ANALIZA faznih premen med SEGREVANJEM THERMO-METALLURGICAL ANALYSIS of phase transformation during HEATING NE NO Ali sta globina in oblika avstenitnega sloja sprejemljivi? Acceptable depth and shape of austenised zone? DA YES Prikaz: porazdelitve magnetnega polja in notranjih toplotnih izvorov, temperaturno polje obdelovanca, porazdelitev mikrostrukturnih faz v segretem sloju. Displays of: distribution of magnetic field and the internal sources, workpiece temperature field, heated zone phase distribution. OBRNJENO MODELIRANJE: izračunavanje koeficienta prenosa toplote iz merilnih rezultatov INVERSE MODELLING: calculation of heat transfer coefficient from measured values TERMOMIKROSTRUKTURNA ANALIZA faznih premen med GAŠENJEM na podlagi faznih diagramov čas-temperatura-transformacija THERMO-METALLURGICAL ANALYSIS of phase transformations during QUENCHING based on time-temperature-transformation diagrams NE NO Shranjevanje Store x Ali je dosežena površinska trdota brez odstopanj? Satisfying surface hardness without flaws? DA YES________________ KONEC END Prikaz: potek trdot v zakaljenem sloju, porazdelitev faz v zakaljenem sloju. Displays of: hardness profile of the hardened zone, phase distribution into hardened zone. Sl.1. Algoritem simuliranja indukcijskega kaljenja Fig. 1. Induction hardening simulation algorithm 8 Sg"ins(5)[J)[M]! ma stran 270 Razvoj modela krmilnega sistema - The Development of a Control System Da bi določili doseženo globino avstenitizacije, izračunamo temperaturno polje z upoštevanjem faznih premen pri hitrem segrevanju v časovno-temperaturnem diagramu avstenitizacije (TTS) pri podanem izhodiščnem mikrostrukturnem stanju. Če je dosežena globina pregretja neustrezna, se znotraj določenih meja najprej spremenijo parametri segrevanja (delovna moč induktorja, trajanje, pomik), šele nato spremenimo velikost in obliko induktorja. Z upoštevanjem temperaturne porazdelitve po procesu segrevanja, se izvedeta simuliranje in optimizacija gašenja. Za natančnejše določanje hitrosti ohlajanja je treba poprej razrešiti inverzni termodinamični problem [6] in izračunati spremembo koeficienta prestopa toplote a (W/m2K) v odvisnosti od temperature. Z uporabo faznih diagramov TTT in enačb fazne kinetike se izračunajo krivulje ohlajanja in po njih nastala mikrostruktura in njena trdota. Ta postopek je uporaben v primeru enojnega indukcijskega kaljenja. Za simuliranje je treba hkrati analizirati indukcijsko kaljenje, segrevanje in hlajenje. Zaradi napak v izračunavanju lastnosti materiala in nenatančnosti matematičnega modela procesa, je potrebna eksperimentalna potrditev modela. Izvedemo jo s snemanjem časovnega spreminjanja temperatur med procesom in z merjenjem dosežene mikrostrukture in trdot po kaljenju. Pred podrobno raziskavo in optimizacijo postopka za novo obliko obdelovanca in induktorja je priporočljivo potrditi model [7]. Overitev ni potrebna, če uporabimo podoben induktor ali obdelovanec. Modeliranje in simuliranje je priporočljivo izvajati s posebnim programom, ki ga lahko razširimo z lastnimi moduli. Za vsakdanjo tehnično uporabo in preliminarne raziskave zadostujejo enodimenzionalni računalniški programi (samo za reševanje elektromagnetnih in termodinamičnih problemov). Drugi korak simuliranja se izvaja z dvodimenzionalnimi in tridimenzionalnimi programi, ki so natančnejši pri načrtovanju in simuliranju [7]. Uporaba računalniških programov ne izključuje sodelovanja s tehnologom za indukcijsko kaljenje, ki mora uporabljati lastne izkušnje in intuicijo med izvajanjem kritičnih progamskih korakov (posamezni izbor po ustrezni analizi). Na ta način dosežemo optimalno temperaturno in mikrostrukturno porazdelitev v najkrajšem času in z najmanjšo potrebno močjo. Po določitvi geometrijske oblike induktorja, vrste sredstva za gašenje in intenzitete gašenja, se parametri indukcijskega kaljenja shranijo v bazo podatkov za krmiljenje procesa in izhodiščno tehnološko bazo. Izstopne veličine simulacijsko-optimi-zacijskega programa, ki se hkrati postavljajo kot referenčne veličine krmiljenja, so prikazane v preglednici 2. In order to determine the achieved depth of austenitization, the temperature field must be calcu-lated. All the phase transformations, according to the Time-Temperature-Austenitizing diagrams, for a given initial microstructure must also be taken into account. Should an unsatisfactory depth of austenitisation be reached, initially the parameters which relate to heat-ing (the power, voltage or current of the induction coil, the heating time, or scan speed) would be modified, within their boundaries. Should these modifications prove inadequate, the size and the shape of the induc-tor must be altered. Starting from the temperature distribution after heating, the quenching phase is simulated and optimized. In order to exactly establish the rate of cooling, after solving the inverse thermodynamic problem first, the alteration of the heat transfer coef-ficient a (W/m2 K) which depends on the temperature has to be calculated [6]. The cooling curves are calculated using the phase transformation and the phase kinetics Time-Temperature-Transformation diagrams. This procedure is suitable in the case of single-shot induction hardening. For simulation the scanning induction hardening, heating and cooling must be analyzed simultaneously. Because of errors in the calculation of the properties of the material and a faulty mathematical model of the process, an experimental confirmation of the model, by recording the time-sequence tempera-tures during the process as well as the obtained micro-structure and hardness after treatment, becomes nec-essary. It is advisable to verify the model before any detailed research and optimization of the procedure for a new shape of workpiece or inductor is under-taken [7]. This is not necessary for a similar inductor or workpiece. To execute a new model or simulation it is advisable to use a special software program which is expanded with self-development modules. For everyday technical use and preliminary research 1-D computer programs are adequate (for solving only electromagnetic-thermodynamic problems). The next simulation step is done via 2-D and 3-D programs for better predictability and a more accu-rate simulation. The use of computer programs does not, however, exclude the induction hardening tech-nician, who must rely on his experience and intuition (making choices after adequate analysis), in the criti-cal programming steps, to achieve the optimal temperature field and microstructure distribution at the surface layer, in the shortest time with the minimum consumption of power. After the inductor geometry has been determined, the parameters of the induction quench hardening are stored into the process control database and the technological initialization base data. The application range of the simulation-op-timization program, which is also used as the reference range for the controller, is illustrated in Table 2. | gfin=i(gurMini5nLn 99/8 stran 271 I^BSSIfTMlGC F. Cajner - J. Grilec - D. Landek Preglednica 2. Izstopni parametri optimizacijsko simulacijskega programa, ki so hkrati krmiljene veličine med izvajanjem procesa indukcijskega kaljenja in mesta merjenja teh parametrov Table 2. Application range of the simulation-optimization program also used as the range of control in the induction hardening process and their measuring points IZSTOPNE KRMILJENE VELIČINE APPLICATION CONTROL SCOPE Generator in induktorska tuljava Power supply and inductor coil Vpenjalni in pomični sistem Workhandling system Sistem za gašenje Quenching system Obdelovanec Workpiece Lega obdelovanca v induktorski tuljavi Position of workpiece within the induction coil X Vhodna moč induktorske tuljave Induction coil input power X Tok in napetost induktorske tuljave Coil current or voltage X Čas segrevanja Heating time X Hitrost pomika obdelovanca Workpiece scanning speed X Koncentracija in čistost sredstva za gašenje Concentration and purity of the quench media X Tlak in pretok sredstva za gašenje Quench media flow and pressure X Temperatura sredstva za gašenje Quench media temperature X Površinska temperatura obdelovanca po postopku gretja Workpiece surface temperature after heating process X Globina zakaljenega sloja, ki jo izmerimo z vrtinčnimi tokovi Depth of workpiece surface hardening verified by eddy current testing X 2 KRMILNI SISTEM DELOVNE ENOTE ZA INDUKCIJSKO KALJENJE Računalniško podprt krmilni sistem je zasnovan na merjenju krmiljenih parametrov procesa in primerjavi z referenčnimi parametri. To je osnutek krmiljenja procesa s t.im. “zapisom procesnih parametrov” (procesni diagrami) optimalno izvedenega procesa. Če kateri od opazovanih parametrov izstopi iz tolerančnega polja, krmilnik signalizira stanje procesa in zahteva njegovo prilagoditev referenčnemu procesu. Znotraj tolerančnega polja krmilnik sam usklajuje potrebne parametre procesa [8]. Pri indukcijskem kaljenju se dandanes, tako kakor pri drugih običajnih postopkih kaljenja, za krmiljenje moči induktorja, premik obdelovanca (ali induktorja) in parametre gašenja, uporabljajo programljivi logični krmilniki (PLK). Običajno se opremi za indukcijsko kaljenje doda večji mikroprocesor. Referenčni (krmilni) parametri in preostali podatki, potrebni za delovanje enote za 2 THE OPERATING SYSTEM OF THE INDUC-TION HARDENING CELL The computer driven control system is based on the comparison between the range of tolerances of the process and the size of the frame of references. This is the process conducting concept according to the so called “recorded process range” (process dia-grams) of the optimally conducted procedure. As soon as one of the elements of the observed range steps out of the field of tolerances, a controller signals the status of the procedure and instructs its adaptation to the process frame of references [8]. The execution of induction as well as con-ventional hardening processes use programmable logical controls (PLC) for the operation of the power of inductor, the mobility of the workpiece and the parameters of quenching. It is customary to add to the induction hardening equipment a host-micropro-cessor. The operating range and other information for the functioning of the system are programmed into the operation database. They are programmed 99-7/8 grin^SfcflMISDSD I ^BSfiTTMlllC | stran 272 Razvoj modela krmilnega sistema - The Development of a Control System indukcijsko kaljenje, so shranjeni v operacijski bazi podatkov, iz katere jih v realnem času in po potrebah nadziranja procesa razbira enota PLK. Zaradi obdelave signala na digitalnem računalniku morajo biti analogni parametri poprej spremenjeni v digitalne z uporabo A/D pretvornikov na kartici PLK. 2.1 Diagnostika procesa Pred začetkom delovnega kroga je treba overiti stanje in delovne parametre vseh podsestavov delovne enote. V primeru manjših in starejših delovnih enot diagnostiko procesa izvaja operater enote. Ob izvajanju poprej računalniško simuliranega indukcijskega kaljenja je nujno potrebno avtomatsko krmiljenje delovnega kroga ob spremljanju minimalnega števila delovnih parametrov na zaslonu (video display terminal - VDT). Primer tipičnega avtomatskega diagnostičnega algoritma delovne enote za indukcijsko kaljenje za delo v avtomatski proizvodni liniji prikazuje (slika 2) ([8] in [9]). into the PLC according to the real time needed for the execution of the procedure. Because of the com-putation of the signal on a digital computer (measur-able information in the feedback), analog signals have to be first converted into digital via an analog/digital converter-card on a PLC. 2.1 Process diagnostic Before the start of the work cycle, it is nec-essary to verify the condition and the functionality of all the supporting parts of the work cell. In the case of smaller and older work cells the diagnostic work is performed by the operator of the cell. To first conduct a computer simulation of the induction hard-ening process, an automated work cycle has to be initiated observing the minimal number of operating functions on a VDT (video display terminal). A typi-cal diagnostic algorithm for an induction hardening work cell, designed for an automated production line, is shown in Fig. 2 ([8] and [9]). Ali so vse okvare in pomanjkljivosti odpravljene? \ ZAČETEK delovnega kroga Have all failures and \ START work cycle shortcomings been eliminated? KRMILNI SISTEM: - določitev parametrov moči induktorja med delovnim ciklusom, - določitev hitrosti pomika, - določitev pretoka, tlaka in temperature izbranega sredstva za gašenje, - določitev dovoljenega odstopanja površinske temperature obdelovanca med segrevanjem. CONTROL SYSTEM: - establishing induction coil power, - establishing scan speed cycle parameters, - establishing quench flow, pressure and temperature of the chosen media - establishing the workpiece surface temperature tolerances during heating. Napačno Faulty Pravilno: začeti proces ali nadaljevati delo Correct: start process or continue work PREVERJANJE STANJA: - nastavitev premika, - nastavitev hitrosti vrtenja obdelovanca, - pregled delovanja črpalk, - pregled mazalnega sistema, - temperatura sredstva za gašenje, - izbira želenega indukcijskega gretja, - prepustnost vhodnega in izhodnega tekočega traku, - druge delovne karakteristike. STATUS CHECKING: - setting the scanner limit switches, - setting the rotation speed of workpiece, - the proper functioning of pumps, - the proper functioning of lubrication, - the quench media temperature, - choosing desired induction cycle, - congestion at the entrance and exit of the conveyor belt, - other work characteristics. Sl. 2. Diagnostični algoritem za indukcijsko delovno enoto Fig. 2. Representation of the diagnostic algorithm for the induction work cell stran 273 BCšD9 F. Cajner - J. Grilec - D. Landek Pred začetkom delovnega kroga diagnostični sistem preveri stanje delovne enote in izvede primerjavo znanih parametrov z vnesenimi. Primerjava se izvaja tudi med procesom kaljenja. Če odstopanja parametrov presežejo vnaprej določene meje, sistem obvesti operaterja in zahteva njegovo posredovanje pri reševanju nastalega problema. 2.2 Krmilni algoritem V večini delovnih enot za indukcijsko kaljenje nadzorujemo dva parametra: relativni premik med induktorjem in obdelovancem ter moč indukcijskega generatorja. Drugi parametri enote ostanejo nespremenjeni oziroma jih skušamo ohranjati nespremenjene. Krmiljenje lahko izvajamo ročno (z nastavljanjem ustreznih potenciometrov) ali avtomatsko (spreminjanje krmilne napetosti, dovedene z računalnika prek D/A pretvornika na kartici PLK). Krmilne napetosti, podane z računalnikom, običajno pripravljamo s prosto izbiro krmilnih operacij ali pa jih pripravljamo kot vhodne podatke, pridobljene iz datotek simulirnih programov po določenem operacijskem zaporedju. Pri enostavni krmilni zanki se razbiranje vhodnih podatkov iz A/D pretvornika izvaja diskretno. Po izvedbi krmilnega algoritma se na D/A pretvorniku pojavijo novi podatki. V ozadju teh dejavnosti lahko računalnik izvaja druge opravke, npr. prenos in obdelavo podatkov. Diskretizacija omogoča ustavitev glavnega uporabniškega programa s skokom na postopek za ustavitev krmilnega algoritma. Princip dela za ustavitev je shematsko podan na sliki 3. Before the start of the work cycle, the diag-nostic system verifies the status of the work cell, and compares the existing parameters with the new ones. In the where case the new parameters exceed the de-fined parameters, the operator is called and asked to solve the problem. 2.2. Control algorithm In most conventional work cells for induc-tion hardening the operation is based on two variables: the scan speed of the intake mechanism and the power of the induction generators. Other aspects of the work cell are made unalterable or are main-tained as such. The operation can be manual (an ad-justment of corresponding potentiometers) or automatic (altering the control voltage via computer through the D/A converter on the PLC card). Con-trolled voltages fed by the computer are usually program generated with a free choice in a controlled operation, or generated through the input of data obtained from databases of simulation programs in sequential operation. In a basic control loop the input of data from the A/D channel is performed during selectivity, and after the execution of the control algorithm new information is fed into the A/D channels. In the background during these operations, the computer can perform other tasks such as the transfer and organization of data. Se-lectivity enables the interruption of the main running program in order to leap to the routine executing of the control algorithm. The principle of performing the routine interruption is illustrated in Fig. 3. ZAČETEK START Uporabniški program Communication program / Inicializacija \ aparaturne opreme Hardvare initiation Digitalni vhod/izhod , Digital input/output , Komunikacijski program za povezavo računalnika z okoljem Interface of computer with environment Sl. 3. Diagram poteka programa z uporabo prekinjevalnega postopka Fig. 3. Program flowchart with interruption routine 8 &nnBjfokJ][p)l]Olf|ifrSO | | ^SsfirWEIK | stran 274 Razvoj modela krmilnega sistema - The Development of a Control System Med programiranjem krmilnih aplikacij je treba posebno pozornost posvetiti vodenju sistema v realnem času, zbiranju podatkov z vhodov A/D pretvornika, njihovi obdelavi in na podlagi tega krmiljenja krmilnih parametrov prek izhodnih kanalov D/A pretvornika. Krmilne aplikacije je priporočljivo izdelati v programskem jeziku, ki je soroden zbirnemu jeziku (assembler) in ki hkrati vsebuje tudi lastnosti višjih programskih jezikov (programski jezik C in njegove nadgradnje). Takšni programi so prenosljivi, njihove izvirne kode pa se brez sprememb lahko izvajajo na različnih računalnikih in z različnimi operacijskimi sistemi. Reševanje problemov pri krmiljenju se izvaja z uporabo podprogramov, ki jih lahko logično poenotimo pri gradnji krmilnih programov. Poenostavljena shema digitalnega krmiljenja procesa (izhodna moč indukcijskega generatorja in premik obdelovanca) je prikazana na sliki 4. Premik obdelovanca Workpiece scan speed Moč induktorske tuljave Power of the induction coil During the programming of control applications special attention should be paid to the con-trol of running the system in real time, to gathering information from the A/D input, its treatment and on the basis of this perform the control scope through the output D/A channels. It is recommended that the control applications should be performed using a program language which is close to that of the assembler which has the ability of many languages, similar to human lan-guages (e.g. program language C, or C++). Such pro-grams have a very high degree of transferability and the resultant codes can be used with various computers under different operational systems. The con-trol program is produced by the use of subprograms and their logical unification. For the simplification of the digital process control (e.g. the outgoing in-duction generator power and the workpiece scanning speed) see Fig. 4. Površinska temperatura obdelovanca Surface temperature of workpiece D/A pretvornik D/A converter Ura za realni čas Real time clock Sl. 4. Poenostavljena shema digitalnega krmiljenja procesa Fig. 4. The simplification of the digital process control diagram 2.3 Problemi uvajanja digitalnega krmilnega 2.3. Problems in the implementation of the digital sistema control system Digitalni krmilni sistemi so diskretni sistemi v pogledu amplitude in časa. Vhodno izhodni parametri digitalnega krmilnega sistema lahko zajemajo le določene celoštevilčne vrednosti, katerih razpon je določen z A/D in D/A pretvorniki. Te pretvornike je treba izbrati tako, da njihove karakteristike (hitrost, ločljivost) omogočajo krmiljenje procesa v realnem času. Z namenom, da bi omogočili krmiljenje z uporabo računalnika je eden od prednostnih problemov povezava računalnika z realnim indukcijskim procesom. Ker računalnik deluje pod nizkim energetskim nivojem (istosmerna napetost do 12 V), ga moramo z izoliranimi ojačevalniki galvansko ločiti od indukcijskega procesa (napetosti anode visokofrekvenčnega generatorja znašajo tudi do 12 kV). Digital control systems are discrete in terms of time and amplitude. The input/output power of a digitally controlled system can accept only integers whose support is defined by the A/D and D/A converters. The converters should be chosen based on their ability to perform the control process (speed, resolution) in real time. In order to make the computer control possible, the problem of the link-up between the computer and the real induction hardening pro-cess becomes a priority. Since the computer func-tions only at low energy levels (direct current of up to 12V) it has to be completely insulated and well separated from the induction process (the power of a HF generator anode can reach levels of 12 kV). gfin^OtJJlMlSCSD 99-7/8 stran 275 |^BSSIrTMlGC F. Cajner - J. Grilec - D. Landek Pri diskretizaciji signalov moramo veliko pozornosti posvetiti hitrosti vzorčenja merjenih parametrov z namenom, da bi diskretizirani signal ustrezno ponazoril stalni signal. Pogosto je treba prilagoditi krmilni signal (z ojačitvijo na potreben energijski nivo), da bi lahko vplivali na objekt krmiljenja v skladu z algoritmom krmiljenja in vektorjem referenčnih parametrov. 3 SKLEP Za kvalitetno indukcijsko kaljenje je treba analizirati procese segrevanja in ohladitve z računalniškim simuliranjem in zagotoviti avtomatsko krmiljenje celotnega procesa. Zaradi pospešitve tehnološke priprave pri oblikovanju induktorja zadošča simuliranje segrevanja obdelovanca z eno od uporabnih numeričnih metod s komercialno razvitimi enodimenzionalnimi računalniškimi programi. Za napovedovanje površinske trdote in porazdelitve zaostalih napetosti po kaljenju je treba simulirati nastale fazne premene in mehanske napetosti pri gašenju, kar pomeni zapleteno nalogo in terja veliko računalniškega časa ter uporabo dvo- in tridimenzionalnih programov. Simulirni programi se izkažejo za koristne pri uporabi oblikovno podobnih ali enakih obdelovancev, za katere je potrebno popolno razumevanje fizikalnih pojavov v procesu in pravilno izvedbo simuliranja. Pomemben prvi pogoj za natančnost simuliranja je tudi pravilna izbira robnih pogojev in dobro poznavanje lastnosti materialov obdelovancev. Za simulirne programe je treba organizirati operativne podatkovne baze, ki se uporabljajo med izvajanjem programov in za shranjevanje rezultatov izračunov. Dobro organizirane podatkovne baze rabijo kot vir znanja in pridobljenih izkušenj pri vsakem novem reševanju problemov indukcijskega kaljenja. Z uporabo računalniških simuliranj je čas projektiranja postopka indukcijskega kaljenja znatno krajši. Induktor, oblikovan za določen obdelovanec, ima lahko, poleg specifične oblike indukcijske zanke, tudi koncentrirana mesta magnetnega pretoka, kar zahteva razvoj posebnih diagramov sprememb procesnih parametrov in ustrezni krmilni algoritem delovne enote. Izhodni parametri simulirnega programa, ki definirajo procesne diagrame (npr. spremembe delovne moči generatorja in spremembe premikov obdelovanca med delovnim krogom) zahtevajo avtomatsko krmiljenje z uporabo PLK. Za diagnostiko delovanja indukcijske enote in za spremljanje parametrov procesa je koristno krmilne parametre prikazati na zaslonu. 8 ^nnatäüllMliBilrSO | ^BSfirTMlliC | stran 276 When selecting of the signal, special attention has to be paid to the speed induced pattern of the mea-sured volume so that the selected signal matches closely the continuous signal. It is often necessary to approxi-mate the controlling signals (amplifying them to reach the required energy level) in order to affect the con-trolled system so that it conforms with the algorithm of control and the vector of the reference parameters. 3 CONCLUSION For quality quench hardening induction, it is necessary to analyze the heating and quenching operations by means of a computer and insure the automatic control of the entire process. To speed up technical preparations for the shaping of the inductor, it is sufficient to simulate the heating of the sample workpiece with one of the available numerical methods and with the help of some commercially developed 1-D computer pro-grams. To predict the surface hardness and the profile of residual stresses after hardening, a simulation of the resulting phase transformations and mechani-cal stresses at the quenching stage become neces-sary. This is a complex task requiring considerable computer time and 2-D and 3-D programs. Simulation programs are usually well suited for a selected group of similar or identical tasks. It is, however, necessary to completely understand the physical outcomes of the process in order to design and conduct a successful operation. The important preconditions for an accurate simulation are the set-ting up of an adequate framework and knowledge of the material properties of the sample. For simulation programs, the operative database must be organized for the servicing of the program and storing of the results of the calculations. By organizing a database it is possible to classify a system of knowledge with each solution to an induction hardening problem, that provides the simulation program with elements of learning. Using computer simulation, the time for the design of the induction harden-ing operation can be significantly shortened. The in-ductor, formed for a concrete task other than the spe-cific induction angle shape, could have concentrators and magnetic flow screens that demand specifically developed diagrams, changed processing parameters and a compatible work cell control algorithm. The application scope of simulation programs that define process diagrams (e.g. the change in the working power of the generators and the changes in the mobility of the sample during the work cycle) re-quire an automatic control and a PLC driven process. For the diagnosis of the work of the induction cell, as well as for the observation of the process parameters, it is useful to show the control parameters and the metering scope with a VDT diagram. Razvoj modela krmilnega sistema - The Development of a Control System Krmiljenje znanih indukcijskih sistemov starejše izvedbe z ročnim in polavtomatskim krmiljem je mogoče posodobiti z uporabo ustreznih krmilnih algoritmov. Pri novih in sodobnih indukcijskih sistemih se bodo simulirni programi uporabljali predvsem za hitro dimenzioniranje induktorjev in za definiranje optimalnih procesnih parametrov indukcijskega segrevanja oz. kaljenja. The existing induction hardening equipment of an older generation with manual or semi-automatic controls could be made more reliable by adapting ap-plicable control parameters and by designing an ad-equate control algorithm. When purchasing new and contemporary induction equipment, future state of the art programs could be built-in for a successful and quick sizing of the inductors and for defining the optimal processing parameters for high frequency hardening. 4 LITERATURA 4 REFERENCES [1] Hassell, P.A., N. V. Ross (1994) Induction heat treating of steel. ASM Handbook Part 4. 9th edition, Metals Park, Ohio, USA, 164-202. [2] Liščič, B., Stupnišek, M., Cajner, F., T. Filetin (1992) Toplinska obradba - praktikum. FSB Sveučilišta u Zagrebu. [3] Rudnev, V.I. et. al. (1997) Induction heat treatment. Steel heat treatment handbook, ed. by G. E. Totten, M. A. H. Howes, M. Dekker Inc. USA, 765-871. [4] Kelly J.B. (1995) Intelligent induction hardening. Advanced Materials & Process, 12/95, 36Q-36R. [5] Schopfel, A., K. Strorzel (1997) Optimization of process parameters for induction heat treating by means of numerical simulation. Proceedings of the 17th Heat Treating Society Conference and Expositions, and 1st International Induction Heat Treating Symposium, 15.-18. September, Indianapolis, Indiana, USA, 595-600. [6] Liščič, B., Tensy, H, W. Luty (1995) Theory and technology of quenching. Springer-Verlag. [7] Nemkov, V.S. et. al. (1997) Computer simulation on effective creative tools for development of induction heat treating processes. Proceedings of the 17th Heat Treating Society Conference and Expositions, and 1st International Induction Heat Treating Symposium, 15.-18. September, Indianapolis, Indiana, USA, 786- 792. [8] Baines, A.P (1988) Induction heating quality assurance monitoring systems. Report 10th ASM Heat Treating Conference & Expositions in Heat Treatment of Metals 1988.1, 9-10. [9] Myers, R. (1992) Diagnostic - a powerful tool for induction heating. Advanced Materials & Processes, 7/ 92, 41-43. Naslov avtorjev: profdr. Franjo Cajner mag. Josip Grilec Darko Landek Fakultet strojarstva i brodogradnje Sveučilišta u Zagrebu Ivana Lučiča 5 10000 Zagreb, Hrvaška Prejeto: 17.11.1998 Received: Authors’ Address: Prof.Dr. Franjo Cajner Mag. Josip Grilec Darko Landek Faculty of Mechanical Engineering and Naval Architecture University of Zagreb Ivana Lučiča 5 10000 Zagreb, Croatia Sprejeto: 15.9.1999 Accepted: stran 277 BCšD9