Dimensionamento e seqüenciamento de lotes de produção na indústria de suplementos para nutrição animal
Resumen
This work studies the integrated lot sizing and scheduling problem in the animal feed
compound industry. The lot sizing problem in this industry consists of deciding which and
how much to produce in each period, in order to minimize overtime and storage costs. The
sequencing problem consists of sequencing the production lots, in order to minimize the
setups (that eat into the available capacity), and to avoid the risks of residual contamination.
The main difference of this problem in relation to the ones in literature is the structure of the
setup times. Using a case study in a company of the sector, four approaches are proposed to
model and solve the problem. The first two are based on the General Lot Sizing and
Scheduling Problem (GLSP) with sequence dependent setup times. The other two approaches
consist of a reformulation of the GLSP model, considering the lot sequencing as an Asymetric
Travelling Salesman Problem (ATSP). Either modeling approach GLSP and ATSP is
proposed for two company strategies related to the cleaning of the production line, called (1)
Independent Sequences , where it is assumed that at the end of each period a complete
cleaning in the production line is carried out; and (2) Dependent Sequences , where the
sequence at the beginning of each period depends on the preparation state of the line in the
previous period (setup carryover). The model GLSP Independent Sequences is solved by the
branch-and-cut method (using the software AMPL/CPLEX), with limited computational time.
To solve the model GLSP Dependent Sequences , besides the branch-and-cut method, two
heuristic relax-and-fix procedures are proposed . To solve the model ATSP Independent
Sequences the subtour elimination method is used. In the case of the model ATSP
Dependent Sequences , as well as the subtour elimination method, the patching subtours
method is used. According to experiments carried out with real data, the models and methods
proposed solve the problem satisfactorily, getting better results that the company. Of the
different approaches proposed, the most appropriate for the problem appears to be the
reformulation ATSP with the patching method and the strategy Dependent Sequences .