About a decade ago, I was asked to propose a definition for Group Technology (GT). I had to consider its origin and how it has been successfully applied for shipbuilding.
When GT was first described in Russia is a bit vague. One account says 1917; another reports sometime in the 1930s. Regardless, both periods were characterized by severe shortages of capital and desperate need to produce more with existing machine tools. As a consequence, most GT literature reflects concerns of people in the machine-tool industry and their obsession with need to identify if a contemplated part, or nearly identical part, was manufactured before. Even a very good GT treatise reflects this bias, but at the same time it warns of need for broader application:
“Although it is relatively simple to define GT, it is difficult to create and install a GT system because of the difficulty in defining clearly how similar one part is to another. For example, parts can be categorized in terms of shape or manufacturing process requirements. These two different viewpoints require a flexible approach to the GT data base and the realization that parochial departmental views of coding may allow some localized cost saving but miss the large corporate savings possible.” (1)
The words “flexible approach” precisely characterize how Ishikawajima-Harima Heavy Industries Co. Ltd. (IHI) of Japan, by 1960, rationalized work in order to apply GT for the fabrication and assembly work required for hull construction. As described in reference (2), hull construction is divided into major manufacturing levels, i.e., parts fabrication, sub-block assembly, block assembly, and hull erection. The first level, for example, is subdivided by:
 parallel-edge parts,
 intricately-cut parts (floors with many cutouts),
 parts with slow curves (some shell plates),
 parts cut from profiles (angles and tees).
At first glance, only shape seems to be the basis for what can be described as separation by problem categories. But the parts represented by  and  are separated from each other despite being produced by the same manufacturing process. In this case the problem addressed is: need for accurate man-hour cost feedback. Man-hours per lineal cutting distances of  are significantly greater than they are for .
For the next manufacturing level, sub-block assembly, another subdivision scheme is employed. Different sub-blocks that can be produced by the same manufacturing process are usually required in varying amounts. The GT basis for their separation is whether or not there is a sufficient quantity of sub-blocks having about the same work content. A sufficient quantity of such sub blocks justifies organization of a workflow with distinct manufacturing stages. Exceptions are shunted for job-shop processing. When shifting from level to level, as well as within each manufacturing level, the bases for GT classifications change to whatever is most logical for rationalizing the most work.
Thus, the definition for GT that I proposed already existed; it is a simple statement that takes in all of the foregoing: “…the logical arrangement and sequences of all facets of company operations in order to bring the benefits of mass production to high-variety, mixed-quantity production.” (3)
(1) “Toward a New Era in U.S. Manufacturing – The Need for a National Vision,” Manufacturing Studies Board, Commission on Engineering and Technical Systems, National Research Council, National Academy Press, Washington, DC, 1986, ISBN 0-309-03691-7, p. 112.
(2) “Product Work Breakdown Structure,” National Shipbuilding Research Program, November 1980, Revised December 1982 (NSRP-0164).
(3) “Group Technology: A Foundation for Better Total Company Operation,” G.M. Ransom, McGraw-Hill, London, 1972.