Jose P. Garcia-Sabater

Material Requirement Planning with fuzzy constraints and fuzzy coefficients

We propose a new fuzzy mathematical programming model for production planning under uncertainty in an industrial environment. This model considers fuzzy constraints related to the total costs, the market demand and the available capacity of the productive resources and fuzzy coefficients for the costs due to the backlog of demand and for the required capacity. The main goal is to determine the master production schedule of each product, the MRP (Material Requirement Planning) for each raw component in each period, stock levels, demand backlog, and capacity usage levels over a given planning horizon. Finally, the proposed model is tested by using data from an automobile seat assembler and compared with other fuzzy mathematical programming approaches. The experiment shows that the proposed model has not got a better behaviour than more simple fuzzy models, but the advantage is that both types of uncertainties, fuzziness and lack of knowledge or epistemic uncertainty can be considered in a model with fuzzy constraints and fuzzy coefficients.

Branch and bound procedures for solving the Assembly Line Worker Assignment and Balancing Problem: Application to Sheltered Work centres for Disabled

In this paper a new problem called Assembly Line Worker Assignment and Balancing Problem (ALWABP) is introduced. This problem arises in those assembly lines where we have certain limited resources available (normally workers) in which the operation time for every task is different depending on who executes the task, and where there are also some task-worker incompatibilities defined. The problem consists of providing a simultaneous solution to a double assignment: (1) tasks to stations; and (2) available workers to stations. After defining the mathematical model for this problem, a basic Branch and Bound approach with three possible search strategies and different parameters is presented. We also propose the use of a Branch and Bound-based heuristic for large problems and analyse the behaviour of both exact and heuristic methods through experimental studies. Finally the implementation of these procedures in a Sheltered Work centre for Disabled-the real environment which has inspired this research-is described. In these centres the adoption of assembly lines provide many advantages, since the traditional division of work in single tasks may become a perfect tool for making certain worker disabilities invisible. Efficiently applying this configuration helps these centres to achieve their primary aim: growth in order to provide more jobs for more disabled people, but always considering the specific limitations that the disabled workers have. In this sense this paper shows one of the possible real applications where Operations Research can help not only to get economic and productive benefits but also certain social aims.

Group technology in a hybrid flowshop environment : A case study

Abstract This paper addresses the problem of products grouping in the tile industry. This production system can be classified as a three-stage hybrid flowshop with sequence dependent and separable setup times. Main objective has been to identify a set of families integrated by products with common features. This classification would help Production Managers to minimize changeover time, allowing them to further reduce production times. The basic concept of “exploiting similarities”, taken from the Group Technology (GT) philosophy, has been used to address the problem in a creative way. A new “coefficient of similarity” between each of the products, has been defined and used as a parameter, allowing products to be grouped through a heuristic method. This research has already been applied in the framework of a real case, getting quite positive results (actual reduction in both setup and production costs, easier long-horizon planning and short-horizon scheduling, more accurate set up time estimates for new products, etc.).

Capacity and material requirement planning modelling by comparing deterministic and fuzzy models

A model for the capacity and material requirement planning problem with uncertainty in a multi-product, multi-level and multi-period manufacturing environment is proposed. An optimization model is formulated which takes into account the uncertainty that exists in both the market demand and capacity data, and the uncertain costs for backlog. This work uses the concept of possibilistic programming by comparing trapezoidal fuzzy numbers. Such an approach makes it possible to model the ambiguity in market demand, capacity data, cost information, etc. that could be present in production planning systems. The main goal is to determine the master production schedule, stock levels, backlog, and capacity usage levels over a given planning horizon in such a way as to hedge against the uncertainty. Finally, the fuzzy model and the deterministic model adopted as the basis of this work are compared using real data from an automobile seat manufacturer. The paper concludes that fuzzy numbers could improve the solution of production planning problems.

A Supply Chain Operations Lot-Sizing and Scheduling Model with Alternative Operations

The aim of this paper is to propose an mixed integer linear programming (MILP) model for operations lot-sizing and scheduling (assignment and sequencing) in the supply chain of an international company which produces and delivers customized products through several geographically distributed assembly plants. The model schedules the purchase of raw materials in the various plants considered, the transshipments, shipments to customers and the various operations to assemble the product. The model considers different alternative production operations such as product substitution (upgrading), alternative procurement and transport operations. It also addresses the different lead times associated with these operations. Specific constraints such as space availability on each plant and workforces are contemplated. A novel approach based on the stroke concept is applied to the MILP model to model alternatives.

Coordinating a cooperative automotive manufacturing network: an agent-based model

One of the problems to be solved in manufacturing networks, with several production centers, is the selection of a suitable manufacturer for each component in order to obtain competitive costs while making full use of the networks capacity. A solution is to own redundant information channels which, despite offering the network greater resilience, generate high costs. The coordination of the nodes in the manufacturing network could lower materials and information flows, thus cutting lead times and total costs, and regulating the systems total productive capacity. This work proposes a coordination model that centralizes materials and information flows, and cuts the costs and overall lead times. It also makes the self-adjustment of productive capacity possible.

Cooperative Multisite Production Re-scheduling

One of the main issues in cooperative enterprise planning and scheduling is how to re-assign tasks without involving too many components of every enterprise and implying too many changes in the whole system. We propose a new system that is able to re-schedule tasks in cooperative multisite production automatically avoiding one of the main problems that have schedule programmers that are in charge of two or more cooperative enterprises. The system is based on making virtual groups of machines that perform the same tasks and establishes links between machines from different groups. We will describe the algorithm in detail and we will validate it using a case of study. Results show that our proposal gives better performance.

A decision support system for modelling and implementing the supply network configuration and operations scheduling problem in the machine tool industry

This paper presents a decision support system to simultaneously solve the supply network configuration problem and the operations scheduling problem for the machine tool industry. A novel database structure, which is able to consider alternative operations and alternative bills of material, has been used. An algorithm for complete enumeration to determine all the feasible solutions using stroke graphs is introduced. A multiagent-based simulator evaluates the different key performance indicators that the supply network deals with for each alternative solution (e.g. workload, profits, delivery times, etc.) to determine that ‘satisficed’ by the collaborative decision-making among its members. A case study based on a Spanish company that assembles highly customised machines and tools in several European plants is considered. From the experiments results based on data linked to this industry, it will be demonstrated that the tool is potentially useful for stakeholders and for the central decision-maker to make decisions collaboratively in a multisite context case.

Outreach initiatives operated by universities for increasing interest in science and technology

ABSTRACT Since the 1990s, the low number of students choosing to study science and technology in higher education has been on the societal agenda and many initiatives have been launched to promote awareness regarding career options. The initiatives particularly focus on increasing enrolment in the engineering programmes. This article describes and compares eight European initiatives that have been established and operated by universities (and in some cases through collaboration with other actors in society). Each initiative is summarised in a short essay that discusses motivation, organisation, pedagogical approach, and activities. The initiatives are characterised by comparing the driving forces behind their creation, how the initiative activities relate to the activities at the university, size based on the number of participants and cost per participant and pedagogical framework. There seem to be two main tracks for building outreach activities, one where outreach activities are based on the universitys normal activities, and one where outreach activities are designed specifically for the visiting students.

Economic lot scheduling with deliberated and controlled coproduction

This paper presents an algorithm to define the optimal parameters for deliberated and controlled coproduction in an economic lot scheduling problem setting (DCCELSP). Coproduction is said to be deliberated and controlled because it is possible to decide whether or not to coproduce when all the parameters associated with the process are known. The aim is to determine how to produce two products most economically where deliberated coproduction is an option. For this purpose, a procedure for defining optimal lot periods is introduced. Two models are proposed for this procedure and a numerical illustration is provided to gain insight into their dynamics. The cost advantages of coproduction were found to depend on the relationship between setup and holding costs, production rates, and demand for products. The more similar these system parameters are and the higher the machine usage ratio is, the more favourable coproduction is. Additionally, if coproduction is not deliberated appropriately, costs soar.