Sunday, 18 June 2006

Hybrid Assembly (1/5)

I originally presented this article, "The Design of Hybrid Flexible Assembly Systems", as a guest speaker at the 6th International Conference on Assembly Automation ...

There is a requirement for a special kind of system to assemble products required in modest volumes with a degree of variety.  A system which is as cost effective and efficient as hard automation, whilst providing the flexibility of manual assembly, is called a flexible assembly system. Within such a system, certain product parts may be required at a different rate to other parts. Some operations may require the flexibility and dexterity of a robot, or even manual labour. The resultant system would be a hybrid of many methods of assembly. This article recommends a technique to be used for the design of such a system, with the aid of a case study.


The factory cost of a product is the addition of the manufacturing cost (e.g. casting, moulding, turning) and the assembly cost (e.g. manual, automatic, robotic).  Industrial engineers continually seek new methods to reduce the factory cost of products. The current trend of exploiting cheap labour in developing nations, through “offshoring” creates a challenge for domestic manufacturers in the developed nations.  Between 40 and 60 percent of the factory cost for many products is associated with the labour content. The majority of this cost is incurred during assembly. There are three reasons for this uneven split between labour costs in manufacturing and assembly.

(i) Manufacturing operations are usually done by, or with the aid of, a machine, i.e. turning, milling, drilling, etc. The manufacturing systems designer does not have the wide choice of the assembly systems designer because some degree of mechanisation must be used. It is then a logical extension to further automate the manufacturing process to reduce labour costs.

(ii) New processes have been developed which eliminate many manufacturing operations. Powder metallurgy is an example of such a process.

(iii) Most products are designed to be assembled manually.  This often means that components are of such a design that they cannot be handled by automatic feeders.  Additionally, many assembly insertion operations are too complex to be automated.

The assembly process is one of the last production processes to be successfully automated by theindustrial engineer. However, as much of the factory cost of a product is incurred during assembly, it is this area where great productivity improvements can be made. The design of the assembly system should be undertaken with due consideration of the design of the manufacturing system and of the design of the product. The design of the assembly system, manufacturing system and product should be considered integrally. These three components, when combined, should create a product having the lowest factory cost at the desired level of quality.  The design of a product and it’s associated production system is an iterative process, whereby product design features dictate the design of the production system and the capabilities of the production system determine the product design. The extent to which these actions can be carried out is only limited by the commitment of a manufacturer to a particular production system and product design.

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