Mohamed Essafi

A MIP approach for balancing transfer line with complex industrial constraints

This paper deals with a novel line balancing problem for flexible transfer lines composed of identical CNC machines. The studied lines are paced and serial, i.e. a part to be machined passes through a sequence of workstations. At least one CNC machine is installed at each workstation. The objective is to assign a given set of operations required for the machining of the part to a sequence of workstations while minimizing the total number of machines used. This problem is subject to precedence, exclusion and inclusion constraints. In addition, accessibility has to be considered. Moreover, the workstation workload depends on the sequence in which the operations are assigned because of setup times related to the change and displacement of tools, rotation of the part, etc. It is a novel line balancing problem, and we highlight its particularities by reviewing the close problems existing in the literature. Then, a mathematical model as a mixed-integer program is suggested. A procedure for computing ranges for variables is given. Experimental computations with ILOG Cplex are reported.

A Reactive GRASP and Path Relinking for balancing reconfigurable transfer lines

A line balancing problem for reconfigurable transfer lines with sequence-dependent setup times and parallel machines was studied. These lines are paced and serial, i.e. a part to be machined passes through a sequence of stations. Stations are composed of CNC (Computer Numerical Control) machines. At least one CNC machine is installed at each station. These CNC machines are mono-spindle head machines, hence setup times between operations have to be taken into account. The origins of setup times are various, for example, the necessity to rotate the part, change and displace the tool, etc. Because of setup times, the station workload depends on the sequence in which the operations are assigned to the station. In addition, accessibility constraints have to be considered. The objective consists of assigning a given set of operations as well as machines to a sequence of workstations in order to minimise the total cost of the line. Keeping in mind the industrial importance of this problem and the lack of available methods in the literature tackling it efficiently, we propose a new heuristic based on GRASP combined with Path Relinking. A MIP approach is used to select the sequences of operations on workstations. Numerical experiments are presented and show that the proposed heuristic can provide good solutions even for large-sized instances while requiring a computational time that is fully compatible with a practical application. An industrial case study is also described.

Machining Lines Automation

This chapter deals with automation of machining lines, sometimes called transfer lines, which are serial machining systems dedicated to the production of large series. They are composed of a set of workstations and an automatic handling system. Each workstation carries out one identical set of operations every cycle time. The design of transfer lines is comprised of several steps: product analysis, process planning, line configuration, transport system design, and line implementation. In this chapter, we deal with line configuration. Its design performance is crucial for companies to compete in the market. The main problem at this step is to assign the operations necessary to manufacture a product to different workstations while respecting all constraints (i.e., the line balancing problem). The aim is to minimize the cost of this line while ensuring a desired production rate. After a review of the existing types of automated machining lines, an illustration of a developed methodology for line configuration is given using an industrial case study of a flexible and reconfigurable transfer line.

A GRASP heuristic for Sequence-Dependent Transfer Line Balancing Problem

Abstract This paper deals with an industrial transfer line balancing problem (TLBP) involving specific constraints. The studied lines are paced and serial, i.e. a part to be machined passes through a sequence of stations. At least one CNC (Computer Numerical Controller) machine is installed at each station. As usual with transfer lines, this problem is subject to precedence constraints as well as exclusion and inclusion constraints. Moreover, the station workload depends on the sequence in which the operations are assigned to the station because of set-up times related to the change and displacement of tools, rotation of the part, etc. In addition, accessibility constraints have to be considered, and different types of CNC machines with different characteristics can be used depending on the operations to perform. The objective is to assign a given set of operations, required for part machining, as well as a set of machines to a sequence of stations while minimizing the total cost of the line. We propose here a heuristic based on the GRASP (Greedy Randomized Adaptive Search Procedures) metaheuristic to consider large size industrial cases.