Flexible manufacturing and small batch production

Citation

Saadat, M. (2007), "Flexible manufacturing and small batch production", Assembly Automation, Vol. 27 No. 1. https://doi.org/10.1108/aa.2007.03327aaa.003

Flexible manufacturing and small batch production

Flexible manufacturing has undoubtedly made highly significant impact on the economics of global manufacturing industry since its inception. One of the most basic challenges of a flexible manufacturing system (FMS) is its capability of efficiently allowing automatic changeovers of tools and parts across machining centres in small batches with the ultimate batch size of one. This would require a somewhat infinite degree of flexibility within a product family range, hence producing high expectations that have made justification for its high initial capital investment difficult, particularly for smaller companies. It is much simpler and less expensive to develop flexible manufacturing cells or islands of automation offering solutions in order to partially address bottlenecks in the production line and improve production efficiency. The general manufacturing concepts proposed or developed since 1990s such as agile, holonic or re-configurable manufacturing systems support, complement or even rely on the development of flexible manufacturing. True FMS should deal successfully with any batch size, but as the batch size decreases in any particular production scenario the utilisation of its true capabilities rapidly increases. So where are we now with respect to these capabilities?

One of the major challenges of FMS has been its scheduling problem especially for random machine operations. This involves part and tool movements around the workstations. Intelligent heuristic algorithms, simulation and knowledge- based decision-support systems have been employed to minimise the non-productive tool and part movements towards achieving a more efficient dynamic scheduling. Tool-changing and tool-sharing play central role in the success of FMS and require some smart dispatching rules. Various research efforts to develop either augmented magazine method or magazine carrier method prove to lead to some success. The outcome is the selection of the next operation in the production centre with as many alternatives as possible.

Multi-spindle technology and the possibility of single cycle production using five-axis machining have made significant contribution to flexible manufacturing. However, efficient job transfers within the machining centre depend on the optimal performance of the movement of the employed automated guided vehicles (AGVs). Minimising workstations feed starvation has been shown to cut unnecessary AGV journeys, as against minimising idle/empty AGV times by shortest distance route allocation.

Compatibility of communication between the workstations is another important factor. Open system architecture including compatibility of various fieldbus protocols offer realistic solutions. A client/server model in conjunction with manufacturing message specification has been designed to work independently of the workstations operating systems. It is important to facilitate reliable real-time dialogue between the machine centres which could be assumed to be autonomous and/or decentralised.

Industry has continued to make competitive advantage in developing and using flexible manufacturing. Most applications centre around automotive, aerospace, machine manufacturing and general sub-contracting. Cincinnati Machine's pallet changing control system development, and Airbus's commissioning of an FMS with five-axis horizontal- spindle machining centres, guided vehicle and multi-pallet handling system which can make ten wing rib types are two recent examples of industry investment in this area.

Modular and expandable systems are being developed which require minimum floor space and have large storage facilities. Concurrent multi-tasking has helped the optimisation of operation and scheduling of various elements of flexible manufacturing. It is now possible to have machining cells that operate 6,000 productive hours per year. Efficient small batch production involving a larger range of products and processes is now possible. Flexible manufacturing will greatly enhance its major contribution in the future of global industrial competitiveness if the value of its flexibility and expandability can be re-quantified in more innovative economic terms. This should help provide a wider access to these capabilities by smaller enterprises too.

Mozafar Saadat School of Engineering, The University of Birmingham, Birmingham, UK</I<