Variety-oriented design of rotary production systems

Abstract

The variety oriented design problem for rotary production systems is considered. Given the multiple parts to be produced, the problem is to determine the feasible configurations of the machining system with minimum cost. This problem is modelled as a combinatorial optimization problem. Constraints related to the design of machining units as well as to the precedence and compatibility of operations are taken into account. The optimization methods developed to solve the problem are based on its MIP formulation. An industrial example is presented.

Introduction

Managing variety is a great challenge facing industry today. In order to reduce the expenses related to the initial setup of the system capacities required by related but different items, such as variants of a product family, variety-oriented planning of capabilities and capacities is needed on the manufacturing-side. Therefore, the manufacturing system should be designed to fit the product variety to be produced [1]. Several approaches for variety-oriented design of manufacturing systems were proposed in the literature, mostly for assembly systems [2], [3], [4], [5].

This paper studies variety-oriented design of rotary production systems used for machining parts. In such a production system, parts are sequentially machined on m (1, 2, …, m) working positions. An example of such a position is provided in Fig. 1. A circular transfer is realized from the zero position where the billet is loaded through all working positions. Each finished part is unloaded at the zero position before the loading of the next billet to be processed.

At each working position, several machining modules (spindle heads) can be installed to process the operations assigned to this position. The machining modules can work sequentially or simultaneously on the same part. Sequential machining is realized by the use of turrets. Simultaneous machining is possible if machining modules applied to different sides of the part work in parallel. Such production systems can use horizontal and vertical spindle heads and turrets to access to different sides of parts at a working position.

Such production systems are modular and can be adapted according to the parts to be produced [6], i.e. the fixtures of parts are changed and some spindles are mounted or dismounted if necessary. However, few studies published in the literature on the design of rotary production systems were mostly dedicated to the mass production case [7], [8], [9], [10], [11], [12]. In difference to that previous work, this paper considers the case of the production of different variants of a product family. Therefore, the production system has to be adapted for producing different product models. The design objective is to choose the equipment to be used by the rotary production system such as – turrets (a turret has several machining modules) and spindle heads – to be installed at all working positions. The goal is to minimize the cost of the equipment required for producing all given product variants. The following decisions must be also made: the choice of orientations of parts, the partitioning of the given set of operations into positions and assignments them to the equipment, and the choice of cutting modes for each spindle head and turret.

The developed design approach offers a mathematical model for the description of the part parameters and operations, constraints between operations and machining modules and technological constraints for rotary productions systems (Section 2). With the use of this model, the design problem is formulated as a combinatorial optimization problem. A mixed integer programming (MIP) approach is used to find the optimal solutions. An industrial example is presented in Section 3.