Universal Assembly Fixtures

in the USSR, devices assembled from a pool of interchangeable, reusable, usually standardized or uniform parts and subassemblies and designed for mounting and fastening parts during intermediate processing, assembly, and inspection operations. The system was developed in the 1950’s in the USSR by the engineers V. S. Kuznetsov and V. A. Ponomarev. It is based on the concept of a constant circulation of standard parts and subassemblies within the production process in order to provide efficient technological preparation for the manufacture of single units and experimental and small-series production lots. Such preparation is designed to shorten manufacturing times, increase the precision of finished products, and raise labor efficiency.

Universal assembly fixtures include components having a variety of functions: bases, supports, mounting parts, guides, and fasteners. The components have a dimensional precision of class 2 or better, which ensures interchangeability. In order to provide high wear resistance, the parts are manufactured of high-quality structural, alloy, or tool steel; in many cases they are subsequently heat-treated. Certain structural features of bases and supports, such as grooves, slots, flanges, and apertures, facilitate the assembly of the components into diverse arrangements. When production of a given article or lot has been terminated, the universal assembly fixtures used are disassembled, and the components are reassembled into different arrangements and reused many times for other purposes; they may also be reassembled into their original configuration if the original article is again put into production.

Universal assembly fixtures are “universal” only with respect to their construction method; a completely assembled fixture becomes a specialized, single-purpose tool. The fixtures thus offer not only all the advantages of specialized tooling but also the advantages of convertible tooling (because of the absence of permanent connections). The latter feature results in the repeated use of parts in various combinations for as long as 15–20 years. An individual fixture has a limited lifetime (up to 15 days), but the system as a whole, that is, the total assortment of available parts, functions continuously in the production process.

The number of parts in one set of universal assembly fixtures ranges from 600 to 30,000 components, depending on the range of items produced by an enterprise. The smallest set is sufficient for assembling 300–400 fixtures of average complexity annually. The largest set will produce the same number of fixtures for simultaneous use. Some standardized sets feature T-shaped connecting slots 8 and 12 mm wide. A typical set consists of 20,000 parts of 150 different types (approximately 600 standard sizes) and may weigh as much as 20 tons.

The high cost of the system of universal assembly fixtures imposes additional requirements concerning use of the fixtures. Parts should not be kept tied up for long periods in unused assemblies. If expensive fixtures are used in one plant only, profitability may be lowered; in this case it is more economical to organize rental centers that serve several plants. If the introduction of a system of universal assembly fixtures is economically justified, the original investment may be recovered in two to three years.

Universal assembly fixtures are used in several plants in Czechoslovakia and the German Democratic Republic. Similar systems are also used in Great Britain, the USA, and the Scandinavian countries.