A reactive GRASP and Path Relinking for balancing reconfigurable transfer lines

Abstract

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. IntroductionIn this paper, we study a line balancing problem for reconfigurable transfer lines. A significant investment in time and money is needed to design and manufacture a transfer line for machining a given part or family of parts. Manufacturers have to invest heavily when installing these lines. The cost of the finished products over the lifetime of the line is greatly influenced by this initial investment. Therefore, competitiveness and profitability depend directly on the investment cost and production efficiency determined by the line design. Thus, optimisation is a crucial issue for designing machining lines.For one or several types of products to be machined, designing transfer lines takes several steps. Namely, product(s) analysis, process planning, configuration design, line balancing, dynamic flow analysis and transport system design as well as the detailed design and implementation of the line. Here, a balancing problem for a given line architecture will be considered. A line balancing problem consists of assigning operations to workstations by considering several constraints (such as precedence, inclusion, exclusion, cycle time, etc.) to optimise one or more criteria (e.g., number of machines, cycle time, total cost of the line, etc.).There are several types of transfer lines. The most common are the dedicated, flexible and reconfigurable transfer lines. This article focuses on the reconfigurable transfer lines (RTLs). RTL use is motivated by the increasingly shorter product runs and the need for more customisation. From the beginning...

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