Final assembly of machines usually takes place along conventional lines, a bit like on a construction site. This may make it possible to accommodate lots of different formats – or product variants – but there is always plenty room for improvement with this construction site approach. Sometimes material provision is disorganized, as are tool supplies and staffing. One way to maximize productivity is to switch to cycle-driven (or timed) continuous assembly. Even with machine construction, continuous assembly is undergoing a renaissance, although adaptations are needed depending on the type of industry. It was with precisely this type of switchover that printing machine maker Koenig & Bauer (KBA) asked the Dresden-based Steinbeis Transfer Center for Production Technology and Waste Handling Logistics to suggest a new way to organize its assembly – and minimize idle periods in production.
Assembling small and medium-size batches of machines (designed to accommodate plenty of variants) does not generally work well with continuous or “flow” production. The main reason for this: low volumes and high customization levels. These are high value products, so cycle times are much longer and “ease of assembly” is not always a central concern in production. There are major differences in technology and with huge numbers of variants, assembly times vary substantially. As a result, it had not been possible to use “traditional” continuous assembly production and maximize harmonization between production and the noncyclical assembly process by using identical cycle times on all stations. Until now.
Assembly times vary according to the type of technology being used and the specific product variant. So with cycles normally lasting two to four hours, it is not possible to fill each cycle properly. There are similar variances in output. This leads to idle time between cycles which could be eradicated if assembly flows moved continuously. So the only way to benefit properly from continuous assembly is to change how the processes are organized and totally avoid idle times. The team working on this particular project consisted of experts from Steinbeis, KBA and Schönheit & Partner. They set the number of cycles to two per shift, dictated not by when the shift begins but by the end of each cycle.
Shortening assembly time during individual cycles means that shifts can start later to match individual cycles, or of course finish earlier. As a result KBA introduced flexitime and job rotation in assembly, making production much more flexible, and assembly costs now equate to the actual amount of time people are being productive. Organizing work processes in this way removes the normal problems encountered with new continuous assembly lines. There are also benefits to be gained by using innovative technology, logistical methods and organizational practices.
In the specific case of this printing machine manufacturer, KBA, where a flexible continuous assembly line was needed, there is plenty of room for innovative ideas: assembly consists of 14 linked work stations lined up in a row. Work volumes are predictable but do vary. Printing towers are pieced together on assembly platforms which travel independently, step by step through the work process on all 14 stations. The moving platforms are battery driven and steered by control wire and transponder.
This way material provision is tailored to requirements on each work station, exactly in time with each cycle. Large parts are handled with hoists which are linked to every work station, suspended from a crane arching over the assembly line. These make it possible for a single person to work on each part. Parts are recognized and large components can be loaded automatically in a safe, ergonomic process.
Tools and equipment have also been tailored to the nature of the job on each cycle and are placed within reaching distance on tool trolleys linked to each cycle. The results of the restructuring speak for themselves: even during the ramp-up phase, KBA cut assembly times by 20 per cent. Throughput times have been shortened by 40 per cent. And the company is now working on extracting a further 10 per cent of potential from its serial production.
Prof. Dr.-Ing. Ulrich Günther
Hendrik Schneider
Steinbeis Transfer Center for Production Technology and Waste Handling Logistics (Dresden)
stz205@stw.de
Dr. Frank Junker
Volker Klitzke
Koenig & Bauer AG (Radebeul)
Dr.-Ing. Michael Völker
TU Dresden Institut für Fördertechnik, Baumaschinen und Logistik (IFBL)