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Tehnica mecanica

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Consideratii privind functionarea unui sistem a.c.o. pentru masini-unelte de rectificat


Consideratii privind functionarea unui sistem a.c.o. pentru masini-unelte de rectificat


CONSIDERATII PRIVIND FUNCTIONAREA UNUI SISTEM A.C.O. PENTRU MASINI-UNELTE DE RECTIFICAT


Cuvinte cheie:masini-unelte, rectificare, control adaptiv



Rezumat: A way to improve the performance of _______machine-tool exploatation is the adaptive conduction of then using A.C.O. system.In this essay is analysed the oportunity to use such an technological equipment to ______ some external cylindrical surfaces with traverse ____ . Beeing an complex activity of optimization, this study is realized by simulation way, using the original logical sketches, with electroncal computer.



1. Introducere


It's known the fact that the optimize of the machine-tools working may be done in many ways, one o these is reprezented by adaptive ___________conducere,



based on A.C.C. and A.C.O. systems;off course the most performant way are A.C.O. (Adaptive Control Optimisation)systems, most of them haveing as optimization___________criteriu the procesing cost, [1, 2].

The system that is presented in this project is grafted on a round______ rectificat machine, made to optimize the round external_______rectificat proces with traverse _____avans. Beeing an automatic procesing system, the physiqal achieve of it presuppose an equip of the _______ rectificat machine-tool with a pack of components that can insure the main function working as the automatic systems theory [2, 3] as this:

identification of the actual working statemen of the machine-tool;

permanent optimize of the working conditions;

comand of the various components of the machine.

Off course, the materialize of an A.C.O. system like this suppose a considerable financial support. A way of justification of that investment is simulateing the working of this adaptive system made for the round external_______ rectificat machine-tool.



2. Prezentarea noului concept adaptiv privind functionarea unor masini-unelte de rectificat


To conceive the patern of optimize is needed to simulate on the computer the round external procesing with traverse avans______________, we need to consider the folowing hypothesis:

the purpose of the optimize proces is minimizing the costs of production, according to the research made and presented in the essay [4];

the matemathical pattern of the adaptive processing is designed far an A.C.O. system to be realised with a single control value;

we deem the fact that the variation , in time, of the radial avans______ of the rectificat____ discus is evoluateing by an synusoidal function:

(1)

where URt is theoretical radial acans______( URt = 0, 00025 mm during a time period Δτ = 4 seconds); A - vibrations amplitude (A = 0, 0002 mm); I - current order number, I = 1 20;

suma cheltuielilor cu manopera (Cmp), amortizarea (Cam) si energia electrica consumata (Cen) poate fi inlocuita - pe baza unor cercetari numerice anterior efectuate - printr-o functie exponentiala de forma:

(2)

in care constanta B = 0, 6437, iar exponentul β = 0, 283.

Tinand cont de toate aceste ipoteze, precum si de concluziile desprinse din lucrarea [4], costul prelucrarii prin rectificare, corespunzator unui interval de timp Δτ, devine:

(3)

unde AΔτ reprezinta adaosul radial de prelucrare indepartat in intervalul de timp Δτ, iar constanta CTΔτ este exprimata in functie de uzura admisibila Ua, a discului abraziv, viteza de uzura radiala si viteza de avans transversal, prin relatia:

(4)

Dupa cum se stie, pentru a gasi valoarea vitezei de avans transversal care asigura costul Cmin este nevoie sa se scrie conditiile necesare si suficiente de existenta ale extremelor absolute ale functiei cost:

(5)

Dezvoltand prima conditie rezulta:


(6)

(7)

(8)

(9)

Fig. 1. Schema logica a simularii functionarii sistemului A.C.O.



The estimation calcul_____ of optimal traverse avans_____ speed according to the cost will be:

(10)


With the help of the final expresion we could calculate the begining value of traverse _____ avans speed needed to start the simulation, that is vctr = 0, 532 mm/min.

Also, to be able to conceive the logical sketch, figure 1, and the simulation program of the A.C.O. system working, for the external round_____ (rectificat)machine-tool, is necesary to remind:

a) when the temperature restriction is passed , where vtrΘ meens the limit traverse _____ avans speed value din punct de vedere al solicitarii termice, the traverse sled is retreated to ______ diamanta the tool and is asked for the necesary time for this operation;

b) printr-un bloc de calcul se vor calcula si apoi lista urmatoarele date tehnico-economice:

costul efectiv (adaptat) rezultat in urma activitatilor de optimizare interna;

costal teoretic (neadaptat) ce se obtine in conditii de prelucrare pe o masina-unealta obisnuita;

adaosul de prelucrare radial, aferent rectificarii adaptive;

adaosul de prelucrare radial ce se indeparteaza in acelasi interval de timp, dar printr-o rectificare "clasica".

Au fost efectuate mai multe rulari ale programului, admitandu-se mai multe variante de seturi ale marimilor de intrare. De fiecare data s-au obtinut costuri mai mici de prelucrare in varianta optimizata adaptiv in comparatie cu varianta clasica de rectificare, situatie explicabila prin prisma valorilor mai mari ale vitezei de avans transversal cu care este capabil sa lucreze sistemul A.C.O. Rezulta implicit faptul ca si din punct de vedere al productivitatii prelucrarii noua varianta tehnologica este superioara celei neoptimizate.


3. Concluzii


Pe baza studiului prezentat sintetic in cadrul acestei lucrari, se pot desprinde urmatoarele concluzii:

v    noul sistem A.C.O. este compatibil cu un echipament tehnologic pentru rectificarea cu avans transversal;

v    rezulta costuri mai mici de prelucrare;

v    se asigura o calitate mai buna a suprafetelor rectificate datorita utilizarii unor elemente de identificare capabile sa restrictioneze solicitarea termica a piesei;

v    sistemul A.C.O. permite o exploatare mai rationala a masinilor-unelte ca urmare a optimizarii adaptive a unor parametrii ai regimului de aschiere, ceea ce implicit, conduce la cresteri ale productivitatii prelucrarii.

Rezulta ca din punct de vedere tehnic/tehnologic exista argumente favorabile pentru dezvoltarea ulterioara a sistemelor adaptive, deoarece ele reprezinta echipamente tehnologice superioare masinilor-unelte clasice.



Bibilografie


1. Agullo, M.: Optimisation en fabrication, Cepadues, Toulouse, 2000.

2. Bragaru, A., Picos, C., Ivan N.V.: Optimizarea proceselor si echipamentelor tehnologice. Editura Didactica si Pedagogica, Bucuresti, 1986

3. Ivan, N.V.: Sisteme CAD/CAM, algoritmi si programe, . Editura Didactica si Pedagogica, Bucuresti, 2001.

4. Rosca, D.M.: Aspecte privind optimizarea statica a prelucrarii prin rectificare rotunda exterioara cu avans radial. Al VII-lea Simpozion TEHNOMUS "Tehnologii si produse noi in constructia de masini", Sectia II, Vol. lucrari, p. 82-88, Suceava, 1993.





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