binary patterns and reconfigure them to obtain a block diagonal cluster formation. The rank order clustering algorithm is the most familiar array-based technique for cell formation (King, 1980).

Substantial alterations and enhancements over rank order clustering algorithm have been described by King and Nakornchai (1982) and Chandrasekharan and Rajagopalan (1986). The direct clustering analysis technique has been implemented by Chan and Milner (1982).

Graph Theoretic Approach depicts that the machines as vertices and the similarity between machines as the weights on the arcs. Rajagopalan and Batra (1975) proposed the use of graph theory to form machine cells. Chandrasekharan and Rajagopalan (1986) proposed an ideal seed nonhierarchical clustering algorithm for cellular manufacturing. Graph searching algorithms was demonstrated by Ballakur and Steudel (1987) which select a crucial machine or part according to a pre-fixed criterion.

Srinivasan (1994) implemented a method using minimum spanning tree (MST) for the machine-part cell formation problem.

This article proposes a novel part family identification technique namely SAPFOCS (Simulated Annealing for Part Family using Opitz Coding System) based on metaheuristic approach to investigate the nature of similarities among parts in the families and to describe the effectiveness of the techniques in solving the problem in hand.

## 2.  Problem Definition

Opitz classification and coding system is used in this article which was proposed by Opitz (1970) at Achen Technology University in West Germany. The basic code comprises of nine digits that can be extended by additional four digits. The general interpretations of the nine digits are as indicated in Fig.

1. The first 5 digits are called the form codes and describe the design or the general form of the part and hence aid in design retrieval process. Later, 4 more digits were added to the coding scheme in order to enhance the manufacturing information of the specific work part. These last four digits are called supplementary codes and respectively represent: dimensions, material, original shape of raw stock, and Accuracy of the work part.

The interpretation of first 9 digits are, Digit 1: General shape of workpiece, otherwise called 'part-class'. This is further subdivided into rotational and non-rotational classes and further divided by size (length/diameter or length/width ratio.)
Digit 2: External shapes and relevant form. Features are recognized as stepped, conical, straight contours.

Threads and grooves are also important.

Digit 3: Internal shapes. Features are solid, bored, straight or bored in stepped diameter. Threads and grooves are integral part. Digit 4: Surface plane machining, such as internal or external curved surfaces, slots, splines. Digit 5: Auxiliary holes and gear teeth.

Digit 6: Diameter or length of workpiece. Digit 7: Material Used. Digit 8: Shape of raw materials, such as round bar, sheet metal, casting, tubing etc.

Digit 9: Workpiece accuracy.

All the 9 digits are interpreted numerically (0-9). Examples of a mild steel forged round bar is shown in Fig. 2.