DETERMINAREA CAPACITATII DE PRODUCTIE

Determinarea capacitatii de productie

1. INTRODUCERE

Capacitatea de productie este maximul de productie, cu structura si cantitate stabilita, care poate fi realizata de o unitate productiva, intr-un interval de timp dat si in conditii tehnico-economice optime.

Definitia cuprinde 4 termeni principali, fara de care este incompleta:

- maximum de productie;

- structura si calitate stabilita;

- un interval de timp dat;

- conditii tehnico-economice optime.

Capacitatea de productie se poate referi la:

- un loc de munca;

- la o zona a sistemului de fabricatie;

- la subsistemul de fabricatie;

- la intregul sistem de productie;

- la un domeniu industrial.

Principala relatie dintre capacitatea de productie si volumul productiei este:

Q = C_p · K_u  (1)

unde:

C_p - capacitatea de productie;

K_u - indicatorul utilizarii capacitatii de productie;

Q - volumul de productie fabricata.

In toate cazurile K_u < 1, => C_p > Q.

In legatura cu C_p este necesar sa se observe urmatoarele elemente:

- C_p este un parametru obiectiv care caracterizeaza potentialul productiv al sistemului;

- C_p este independent de volumul productiei;

- ca o conditie, se doreste ca Q sa fie cat mai mare posibil (spre 90% din C_p);

- relatia K_u = 1 nu este posibila, pentru ca in acest caz intretinerea si reparatia masinilor-unelte, la caderi accidentale, ar fi instantanee (imposibil) si costurile ar fi infinite.

Cunoasterea capacitatii de productie este importanta pentru:

- elaborarea planului de productie;

- elaborarea planului de dezvoltare si de investitii (redimensionarea sistemului de productie);

- evaluarea rezervelor nefolosite de catre sistem (acestea sun proportionale cu 1- K_u);

- optimizarea organizarii productiei;

- alaturi de costurile de productie si pragul de rentabilitate, reprezinta un parametru important in negocierea contractelor cu clientii.

2. CALCULUL CAPACITATII DE PRODUCTIE

Relatia generala, valabila pentru diferite tipuri de productie este:

C_p = A·T·I (2)

unde:

A - este caracteristica dimensionala: numarul de echipamente [buc.], volumul util [m³], suprafata de productie [m²];

I - indicatorul de utilizare intensiva [buc/ora], [m³/ora], [t/ora];

T-fondul de timp (perioada de timp considerata), dat uzual in [ore/an].

Exista mai multe componente ale fondului de timp:

F_ta - fondul total anual de timp; F_ta = 365 · 24 [ore/an];

F_tn - fondul total nominal (anual) de timp;

F_tn = F_ta- t_r·24=D·s·h [ore/an]

unde:  - t_r - numarul zilelor de repaus (libere) din an;

- D - numarul zilelor de lucratoare din an;

s - numarul de schimburi pe zi;

h - numarul orelor pe schimb;

F_tef - fondul total efectiv (anual) de timp;

F_tef = F_tn - t_rep= F_tn(1- r) [ore/an]

unde:

- t_rep - timpul planificat de intretinere si reparatii pe an;

- r = 3,5 . 12 % pentru masini-unelte (mediu 6 %).

F_tteh - fondul total tehnic de timp;

F_tteh = F_ta - t_rep

Acesta este utilizat situatiile de "foc continuu", cand se lucreaza tot anul, fara zile libere.

2.1. Capacitatea de productie pentru fabricatia unui singur produs, cu posturi dispuse in paralel

Acest caz este schematizat in figura de mai jos:

2.1.1. Pentru sistemele de fabricatie din constructia de masini

Capacitatea de productie este obtinuta, prin particularizarea relatiei (2), ca raport intre fondul de timp si timpul normat pe unitatea de produs:

unde:

p - numarul de masini-unelte (echipamente) din grup - caracteristica dimensionala;

F_t - fondul de timp pentru o masina-unealta (uzual F_tef);

n_t - timpul normat (norma de timp) pe unitatea de produs, iar 1/n_t este indicatorul de utilizare intensiva (ritmul de fabricatie al unei masini).

F_t este acelasi daca toate echipamentele indeplinesc urmatoarele conditii:

Necesita acelasi timp pentru intretinere si reparatii;

Sunt utilizate acelasi numar de schimburi.

n_t este acelasi daca:

Echipamentele au performante tehnice egale;

Muncitorii (operatorii) au rezultate egale in munca.

Daca F_t si n_t sunt diferite, sistemul de fabricatie trebuie divizat in grupuri cu performante egale. In acest caz relatia (3) se scrie in forma (4).

unde:

- M - numarul de grupuri de echipamente si operatori cu performante egale. Elementele p_i , F_ti si n_ti au aceeasi semnificatie.

2.1.2. Pentru situatiile in care productia depinde de suprafata (chimie, agricultura, logistica, chiar si montaj uneori)

Capacitatea de productie poate fi calculata cu:

unde:

S_u - suprafata utilizata de sistemul de fabricatie;

s_u - necesarul de suprafata pentru unitatea de produs.

2.2. Capacitatea de productie pentru fabricatia unui singur produs, cu posturi dispuse in paralel-serie

Procesul tehnologic este divizat in mai multe subprocese.

In acest caz, fiecare unitate de produs este fabricata pe mai multe locuri de munca , ca in figura de mai jos.;

Pentru determinarea capacitatii de productie a intregului sistem, este necesar sa se calculeze capacitatea de productie pentru fiecare grup de masini, utilizand una dintre relatiile (3), (4) sau (5), dupa caz.

Capacitatea de productie pentru intregul sistem va fi:

(6)

unde:

- C_pG1, C_pG2, . , C_pGg, - capacitatile de productie ale grupelor 1, 2, . , g.

Un caz particular, este acela in care productia este organizata pe linii de productie (serie-paralel), cum este cel de mai jos:

Capacitatea de productie pentru fiecare linie este egala cea mai mica dintre capacitatile de productie a masinilor care compun linia. Spre exemplu pentru linia 2:

(7)

Fiecare capacitate de productie se calculeaza cu relatiile (2), (3) sau (5), in functie de caz. Capacitatea intregului sistem va fi:

(8)

OBSERVATII IMPORTANTE

1. Cazurile precedente sunt aplicabile pentru situatia fabricarii unui singur produs, sau pentru cazul in care se fabrica mai multe variante de produse, asimilabile cu un produs reprezentativ (sau fictiv). Obtinerea produsului reprezentativ a fost tratata intr-un curs precedent.

2. Capacitatea de productie pentru mai multe clase de produse (neasimilabile cu un produs reprezentativ) se poate calcula prin mai multe metode, cele mai folosite fiind:

- metoda coeficientului de timp;

- metoda grupului principal de masini (echipamente).

2.3 Production capacity for many product types and a single product for each workplace (equipment)

By analyzing the flows of production, the fabrication system will be divided in smaller subsystems like in the above types. An example, with 4 fabrication subsystems is presented below.

Fig. 4

Where:

SPF1, . , SPF4 - Semi-product flows for 4 products;

FPF1, . , FPF4 - 4 different finished products;

FSS1, . FSS4 - 4 production subsystems;

FS - fabrication subsystem.

In this situation, the production capacity is calculated for each subsystem (and product) with one of the relations (3), (4), (5), (6) or (8), according to the case.

2.4 Production capacity for many product types and many products for each workplace (equipment)

In most cases, during a whole year, in the industrial factories, many products are fabricated in one workplace. Each product has it's own time fund.

The production capacity calculus must be accomplished by taking into account that all the products must be fabricated. There are many calculation methods.

2.4.1 Method of time fund coefficient (Metoda fondului coeficientului de timp)

This method is based on the time fund distribution (for one equipment or for a group of equipments) for each product, directly proportional to the necessary time for the fabrication of the planned quantities.

The method will be presented by using an example.

The input information and the calculated parameters are presented in the below table. We suppose the enterprise has in fabrication the products A, B, C, and D, by using a group of equipments which have a total annual time fund equal with 141200 [hours/year]. This time fund was calculated by association with one of the cases presented in the chapters 2.1 or 2.2 and by considering that any product can be fabricated in equal conditions.

Table 1

There are other two equivalent methods, more elaborated, which give the same results. These methods are:

Method of representative product;

Method of conventional units.

All of these three methods offer good results if the equipments are replaceable each-other, like machine-tools with numerical control and similar performances.

2.4.2 The method of the principal group of equipments (Metoda grupului principal de echipamente)

We will consider the most general structure for a fabrication system, where we can identify J groups of equipments (E): machine-tools, work-places, etc. with similar performances.

For each group it is calculated the production capacity by using one of the tree methods which were presented in the previous sub-chapter (sub-chapter 2.4.1). The parameter which characterizes the production capacity and the reserves of each group, related with production plane, is the time fund coefficient.

Normally, like the previous paragraphs, the production capacity for all fabrication system is equal with the minimum of the production capacities of the groups. In these methods there are not differences in importance among the equipment groups.

The method of the principal group of equipments takes account by the importance of the groups in the whole fabrication system. The most important equipment group is named "the principal group (PG)" or "ruling group" That group gives the production capacity for the whole fabrication system C_pFS.

Usually, it makes a diagram like below. The diagram is named "balance of production capacities".

Fig. 6

The principal group is established by using the following criteria:

the ratio from the total machine-tools park considering the number and the technological importance

the percentage from the total value of the machine-tools park

The equipment groups which have a production capacity smaller than the principal group are named tight places. These must be eliminated by using technical and economical activities. Several of these are:

Intensive measures for using the internal reserves:

the change of the splintering conditions;

the endowment with tools and devices;

the introduction of new technological processes;

the improvement of organizing the working place.

raising the personnel's skills;

Extensive measures for using the internal reserves:

raising the number of shifts;

reducing the length of time for reparations.

Complex measures:

the co-operation with other enterprises;

the acquisition of new equipments;

the modification of constructive solution of the products.

2.4.3. The production capacity for whole production system

If the production system is composed by many fabrication (sub)systems, the production capacity for whole production system can be calculated by using the same method as it was presented in chapter 2.4.2. The principal group of equipments will be replaced by the principal fabrication (sub)system. On the abscise of the balance of production capacities will be placed all the fabrication (sub)systems of the factory.

It is possible to use even the method from chapter 2.4.1, and in this case the problem is more simple.