Abstract
A lot sizing and scheduling problem prevalent in small market-driven foundries is studied. There are two related decision levels: (1) the furnace scheduling of metal alloy production, and (2) moulding machine planning which specifies the type and size of production lots. A mixed integer programming (MIP) formulation of the problem is proposed, but is impractical to solve in reasonable computing time for non-small instances. As a result, a faster relax-and-fix (RF) approach is developed that can also be used on a rolling horizon basis where only immediate-term schedules are implemented. As well as a MIP method to solve the basic RF approach, three variants of a local search method are also developed and tested using instances based on the literature. Finally, foundry-based tests with a real-order book resulted in a very substantial reduction of delivery delays and finished inventory, better use of capacity, and much faster schedule definition compared to the foundry's own practice.
Highlights
Foundries are common in every region of Brazil, producing many types of products, ranging from simple items for domestic use to sophisticated parts for the automobile and machine tool industries
In order to evaluate the performance of the RF method, we used the solutions and lower bounds obtained by the Cplex 7.1 solver applied to model (1)-(9) in a general purpose branch-and-cut search
The final value of the objective function is gradually accumulated over the T applications of model RH, each of which contributes its period 1 part: N
Summary
Foundries are common in every region of Brazil, producing many types of products, ranging from simple items for domestic use to sophisticated parts for the automobile and machine tool industries. Foundries can be classified as either captive or market-driven. The former tend to be part of large companies, such as car manufacturers, that totally absorb the foundry production, composed of large quantities of a small number of parts with relatively stable demand. Market-driven foundries are generally small or medium sized companies that produce a huge range of items with vastly varying demand. While captive foundries use a small number of different metal alloys, market-driven foundries need to work with a wide variety due to the diversity of their clients. This paper focuses on the problem of planning and scheduling production in small market-driven foundries
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