Materials Supply and Product Descriptions for Assembly Systems - Design and Operation

Doctoral thesis, 1999

This thesis discusses and reports on assembly systems design, concerning manual assembly of complex products involving production with requirement for flexibility in production volumes and product variants. The research is based on more than a decade of work within the Swedish automotive industry focusing on parallel product flows and long cycle time assembly work. The work has been accomplished in close co-operation with the industry based on both theoretical and practical frames of reference dating back to the 1970s. The work has resulted in implemented assembly systems organised in work groups and materials supply by means of materials kitting. Product descriptions have been found to be crucial regarding design of assembly systems including materials supply. An assembly oriented product structure has proved to be a significant key factor in this context. To achieve such a structure is a matter of reforming the traditional (abstract) product descriptions, which are based on and include the general design oriented product structure. Materials kits have proved to be a feasible way to accomplish the materials supply, since the materials kit functions as a work instruction and both materials supply and operator learning are enabled. Thus, materials kits bridge two inter-linked restrictions, for full-scale parallel flow, long cycle time assembly systems. The thesis explains how to reform traditional product descriptions by, for example, introducing a method for assembly systems design. The method is principally based on the information available in the design oriented product structure and utilises the physical components of the product to design intra-group work patterns and materials kits to achieve so-called structural congruence. This congruence is one key factor for the so-called materials kit configuration, which in turns leads to high materials kits functionality and reformed product descriptions. It is also shown that available product variant specifications and product variant identification procedures, applied in line assembly, lead to complex descriptions. Methods that reduce this complexity due to applications in long cycle time assembly are reported. Observed effects of applying such descriptions and methods are foremost described through case studies, which report on observed work pace in long cycle time assembly work and as well as how parallel work groups performed their assembly work. These results illustrate that there does not need to be a contradiction between humanisation of work and efficiency, or between efficiency and flexibility. The use and need of appropriate abstract product descriptions are especially demonstrated through the possibility to utilise assembly oriented product structures as the fundament in design of assembly systems, work instructions and product variant descriptions.