Group Technology

Introduction

Group Technology is a manufacturing philosophy that exploits similarities in the design, fabrication, and assembly attributes of products. A Group Technology (GT) code is an alphanumeric string which represents critical information about the product in a concise manner. Comparing the GT codes of two products is a quick and efficient method for estimating product similarity in selected attributes. GT codes can be used to search a database of products and retrieve the designs and process plans of those products which are similar to a given design, to generate new process plans automatically using a knowledge-based system, and to assess manufacturability of a product design.

GT coding and classification schemes attempt to capture design and manufacturing attributes such as the main shape, size, features of the product, production quantity, and material. A large number of GT coding schemes have been developed for discrete machined parts including MICLASS, Opitz and DCLASS.

Group Technology codes are typically generated manually or interactively by answering a series of questions and applying appropriate coding rules. However, this is a slow and inconsistent procedure which inhibited the widespread use of Group Technology.

A number of automated GT code generation tools have also been developed. Shah and Bhatnagar developed an automated GT coding system based on the Opitz coding scheme for machined parts. The system assigns pre-defined taxonomy codes for each feature of its feature-based CAD system. The generic information captured by the taxonomy codes is used to determine individual feature characteristics and the relationships between features and the entire parts. The GT code generator uses the resulting feature information and Opitz coding rules to generate the GT codes. Henderson and Musti developed a system to automatically generate the DCLASS GT code of rotational products from a 3-D CAD database. This system recognize mechanical features from the part's boundary representation model; it then uses this feature information to generate the GT codes. Chen developed an automated GT coding system that operates on a product design specified in the IGES format. In this system, an IGES file is converted into a custom product definition file which is then transformed into a format from which the GT codes can be extracted. Bhadra and Fischer developed a microcomputer-based Group Technology system to classify and code rotationally symmetric parts.

Discussion

The Group Technology (GT) is a manufacturing philosophy in which parts or other objects (process plans, products, assemblies, tools, etc.). Similar are identified and grouped together to take advantage of their similarities in the various activities of the company (design, manufacturing, purchasing, production planning and control, etc..). According Hyer & WEMMERLÖV (1984) the use of these similarities occur in three ways:

performing similar activities together, thus avoiding loss of time with the changes required to move from one activity to another unrelated (e.g. the manufacturing sequence of two parts with similar characteristics reduces setup time between operations);

standardizing similar and related activities, thereby focusing only on differences necessary and preventing duplication of effort (e.g. reduction of the variety of screws used);

storing and retrieving information efficiently, especially those related with repeated ...